bluuebunny/crossref_metadata_2025 huggingface dataset:
Method of Forming Fine Holes of Near Atomic Dimensions
Authors: Fleischer R. L. , Price P. B. , Walker R. M.
Published: February 2005

A method of forming small holes in certain materials is described. The material is first exposed to massive, high energy particles such as fission fragments and is then immersed in a chemical etching solution which dissolves the damaged material along the paths of the particles. With this technique it is possible to form holes which are as small as 25 Å in diameter and are up to ∼10 μ long. The hole diameters can be increased at will from the minimum size by continued etching. A density of up to ∼1011 holes/cm2 can be attained by a short irradiation in a typical reactor. The holes can be accurately aligned by collimating a beam of fission fragments. Fine holes have been formed in this way in a number of nonmetallic materials including glass, mica, and other silicate minerals.
Use of Gated Image Converters at High Light Intensities
Authors: Stewart George W. , Waniek Ralph W.
Published: February 2005

Pattern reproduction problems arising with the use of image converters operating at high light levels in gated regimes in the microsecond range are examined. Potential gradients developed across the finite resistance of the photocathode are ascertained to be the mechanism causing distortion. Theoretical formulas are derived to describe the photocathode potential for the case of homogeneous illumination and to estimate the influence of such extraneous fields on the electron-optical imaging. Three methods of remedy are discussed, one of which is supported by theoretical and experimental evidence presented in the paper.
Versatile Technique for Measuring Fluorescence Decay Times in the Nanosecond Region
Authors: Steingraber O. J. , Berlman I. B.
Published: February 2005

A new method of accurately recording scintillation pulse contours over several decades is described. Scintillation pulses are analyzed by an apparatus which combines the very fast rise time of a pulse sampling oscilloscope and the digital storage capacity of a multichannel analyzer. A special feature of this technique is its ability to accept, within limits, pulses random in time and amplitude so that fluorescence from samples excited either by pulsed uv radiation, β, or α particles may be analyzed. This apparatus, in combination with a hydrogen flash tube and a monochromator, has been used to measure the decay time of fluorescent solutions as a function of the wavelength of the exciting radiation. Decay time measurements have also been made for various modes of excitation: α particle, β particle, and pulsed uv.
Measurement of Electrostatic Charge on Solid Particles in Solid-Gas Suspension Flow
Authors: Min K. , Chao B. T. , Wyman M. E.
Published: February 2005

A method for measuring the charge spectrum of particles in a solid-gas suspension flow is described. The probe, fabricated of hypodermic needle, gives minimal disturbance to the flow stream. The charge spectrum is obtained by a pulse counting technique. Typical results are presented for glass particles of 80 μ diameter in air stream flowing at 8 m/sec inside an aluminum channel. The charge distribution follows essentially an exponential law and the average charge per particle has been found to be 1.3×10−14C. Practically all particles carried a measurable charge.
Feasibility of Containment of Quantum Magnetic Dipoles
Authors: Heer C. V.
Published: February 2005

The design of a ``magnetic bottle'' for neutral quantum magnetic dipoles is considered. It is shown that atoms or molecules with a magnetic moment and described by a wavefunction ψ(JmJ) may be confined to the interior of a toroid for suitable values of J and mJ for periods of the order of seconds. The magnetic field which is required for containment is obtained by a current distribution which is formed by six current loops symmetrically placed on the toroid surface. Adjacent current loops carry current in opposite directions. For large toroids the magnetic field distribution approaches that of the hexagonal array of linear currents used by Friedberg for focusing magnetic dipoles. The trajectories inside the toroid, the design of an experimental system, and the limitation of the ``magnetic bottle'' are considered. Containment of atomic hydrogen and the metastable states of some gases seem feasible; and the containment of neutrons, other atomic systems, and molecules awaits improved techniques of thermal moderation.
Ultraviolet Recording Microspectrophotometer
Authors: Wagener G. N. , Grand C. G.
Published: February 2005

The design of a scanning and integrating microspectrophotometer for studying the absorption of tissue cells in the wavelength region 2200 to 7000 Å is described. The instrument can be used in three modes: as a double beam system in which the two beams are derived in the image plane of the microscope using a two-hole aperture plate, as a scanning integrator, and as an uv photomicroscope.
Computer for the Abel Inversion
Authors: Yokley C. R. , Shumaker J. B.
Published: February 2005

An electronic analog-type computer is described which performs the Abel inversion on signals detected by a scanning photoelectric spectrometer. This computation is necessary to obtain the radial characteristics of an inhomogeneous light source from the observed ``side-on'' measurements. The amplitudes resulting from a Fourier analysis of the photomultiplier signal are operated upon to produce an electrical signal corresponding to the source intensity at any desired radial distance. This signal can be continuously recorded as a function of wavelength. The optical system used for repetitively presenting the intensity profile of the source to the computer at 100 cps is also described.
Trajectory Tracer for Charged Particles Which Includes Magnetic Fields and Space Charge
Authors: Van Duzer T. , Buckey C. R. , Brewer G. R.
Published: February 2005

This paper presents the theory and design of an analog system for computing trajectories of charged particles in electron and ion guns, where the effects of space charge and magnetic fields are important. Two electrolytic tanks are used for simulation of the total electrostatic and magnetic fields. The wedge-shaped tank used for simulation of the electrostatic fields in axial symmetry contains current sources in the forms of wire probes and inlaid resistive plugs for the introduction of space-charge effects. The magnetic fields to be considered satisfy Laplace's equation and are simulated by specifying boundary conditions on the magnetic scalar potential. A special tank for obtaining accurate results on a thin annular beam is described. A precision analog computer solves the equations of motion with the fields measured in the tanks and controls the servomechanisms which move the field-sampling probes along the trajectory. Some results for high-perveance electron guns are compared with beam sampling measurements on actual guns.
X-Ray Diffractometer for the Study of Liquid Structures
Authors: Kaplow Roy , Averbach B. L.
Published: February 2005

An automatic x-ray diffractometer for the investigation of liquid structures has been built. The specimen is held in a horizontal position. The x-ray source and detector rotate in a vertical plane about the center of the specimen face, maintaining equal angles of incidence and diffraction and a constant d(sinθ)/dt. Precise adjustment devices are provided for the parameters of the diffraction geometry and for a crystal monochromator which may be located in either the incident or diffracted beam. A variety of specimen holders may be used, including a high temperature stage which is designed to minimize condensation of vapors evaporating from the specimen.
Verneuil Crystal Growth in the Arc-Image Furnace
Authors: Halden F. A. , Sedlacek R.
Published: February 2005

The development of an arc-image system for crystal growth, and techniques for obtaining continuous growth of single crystals under controlled atmospheres, are described. Crystals grown include rutile, sapphire, ruby, stabilized zirconia, and ferrites.
Welding Tantalum for High Temperature Applications
Authors: Miller A. E. , Daane A. H. , Habermann C. E. , Beaudry B. J.
Published: February 2005

A device is described which can be used to weld tungsten, tantalum, and molybdenum. The general problem of fabricating tantalum process equipment from tantalum sheet is discussed.
Vacuum-Tight Cylinder Joints and Ball-and-Socket Joints
Authors: Guildner L. A. , Stimson H. F.
Published: February 2005

Two types of vacuum-tight joint have been developed for articulation of the connecting lines of a mercury manometer. The design and construction of each joint are described. The cylinder type has a seal around the circumference of a tube. The exit tube of the cylinder joint can be moved in a plane normal to the joint axis. The ball-and-socket type has a seal around the equator of the ball. The exit tube of the ball-and-socket joint can be deflected 15°. The joints are packed with Teflon and they remain vacuum tight without causing excessive resistance to movement.
Polystyrene-Silica Replica Technique for Relocating Selected Areas for Examination in the Electron Microscope
Authors: Murray Homer L.
Published: February 2005

A sandwich technique is described for fabricating polystyrene-silica replicas for repeated examination of a selected area of a specimen in the electron microscope. Electron micrographs of these repetitive replicas are presented. The technique includes a method for manipulating the specimen grid without slippage and, also, a method for eliminating the difficulty of stripping the preliminary impression from a heavily etched steel surface.
Apparatus for Determining Ignition Times of Explosives under Vacuum and Various Gases
Authors: Abel James E. , Reitzner Bruno
Published: February 2005

A new instrument for obtaining induction times of explosives under vacuum and different atmospheres is described. The outstanding feature of the instrument is an automatic dropping mechanism which permits 50–100 ignition times to be determined without breaking the vacuum. Ignition times down to the millisecond range can be determined.
Absolute Intensity Measurements in Small-Angle X-Ray Scattering
Authors: Weinberg D. L.
Published: February 2005

The absolute intensity of small-angle x-ray scattering has been measured by two methods—comparison with a beam transmitted through a series of similar attenuators, extrapolated to the case of no attenuators, and comparison with the scattering of air—with good agreement. Some reproducible substances are calibrated as standards at small angles and some also at larger angles, in the range accessible to the diffractometer. Brief interpretations are given of the small-angle scattering; that of water is consistent with theory. The long-range density fluctuations of vitreous silica are found to be mainly those frozen in at the glass transformation. The absolute scatterings are compared with Katz's unpublished small-angle standardization and with Warren's standardizations of Lucite and vitreous silica by means of high-angle scattering. Katz's measurements of silica and Warren's of Lucite are appropriate for quantitative comparison. They are about 2% higher and 7% lower, respectively, than the present result. Finally, the effect of impurities is derived.
Use of Optical Density Measurements of Thin Films to Determine Vapor Distributions
Authors: Anastasio Thomas A.
Published: February 2005

An experimental study of the use of the optical density of thin films to determine the spatial intensity distribution of metallic vapor is reported. The linearity of the optical density vs film thickness curves of Ag, Au, Cu, Ge, In, and Sn is investigated through the use of thin film wedges. Upper and lower bounds on linearity are given. The lower bound is found to be dependent on deposition rate. Typical distributions for flat molybdenum strip and conical tungsten basket sources are given.
Device for Continuous Isokinetic Aerosol Sampling
Authors: Princen L. H. , Clarenburg L. A.
Published: February 2005

A simple apparatus for isokinetic sampling of aerosol streams has been described. By means of this device it is possible to branch off between 0.4 and 16% of an aerosol stream for continuous isokinetic sampling. An easy method of calibration has been given. The sampling flow was constant within 1%, and no appreciable amount of particulate matter was lost.
Application of the Matrix Method to a Browne-Buechner Spectrograph
Authors: Handdock Roy P.
Published: February 2005

The motion of a group of ions (with respect to the trajectory of one of the ions) in a magnetic field of the form B∼rn may be described by linear second-order differential equations when the displacement, slope, and momentum spread of the ions are small. The general solution may then be written as a matrix operating on the initial conditions. A procedure is described herein for interpreting the paraxial properties of a spectrometer system in terms of the matrix elements. Then it is shown that a similar treatment is applicable when the momentum spread is not small, as in the case of the Brown-Buechner spectrometer. The matrices for the Browne-Buechner spectrometer are derived and interpreted for a more general case than has heretofore been considered.
Enhancement of Signal-to-Noise Ratio by Continuous Averaging: Application to Magnetic Resonance
Authors: Klein Melvin P. , Barton George W.
Published: February 2005

Spectroscopic investigations commonly involve a measurement of power as a function of some external parameters. It is usual, for improvement of signal-to-noise, to modulate the interaction between the radiation and sample and to apply the resulting signal to a synchronous detector followed by an integrating filter and a chart recorder. An extended search for a weak signal may require slow scanning rates and long time constants. Such a combination imposes severe requirements on the stability of the equipment, for any nonstochastic noise can frustrate a single scan by exceeding the dynamic range of the chart recorder. An alternative approach to the problem is to accumulate many relatively rapid scans of the full spectrum so that the signals add coherently whereas the noise adds randomly. The first approach may be termed frequency domain filtering while the latter is termed time domain filtering. Here we report an example of the latter approach employing a multichannel pulse-height analyzer as a storage device. The voltage from the output terminals of a spectrometer (nuclear magnetic resonance or electron paramagnetic resonance) is converted to pulses, the pulse rate being proportional to the voltage. The channels are opened successively in synchronism with the progress of the magnetic field. Thus each channel corresponds to a finite region of the field while the number of counts in each channel is proportional to the time integral of voltage corresponding to that field. In such an arrangement the signal increases directly as the number of scans while the noise increases as the square root of the number. In effect the average response is computed continuously. The great dynamic range, 106 pulses/channel, precludes overloading or saturation effects. Since no long time constants are employed, low-frequency noise is no longer the limiting factor in equipment performance. We present spectra, resulting from many thousands of scans, which demonstrate that signal-to-noise ratios may be enhanced by one to two orders of magnitude without sacrifice of bandwidth.
Photoelectric Skylight Polarimeter
Authors: Sekera Z. , Rao C. R. Nagaraja , Dibble D.
Published: February 2005

A photoelectric skylight polarimeter employing a retardation plate as a polarization modulator with constant angular and linear apertures is described in detail. The operational wavelength range of the instrument extends from the near ultraviolet to the far end of the visible part of the electromagnetic spectrum (∼3000 to 6500 Å). A brief discussion of the possible uses of the instrument is given.
Circular Chevron Diffusion Pump Baffle
Authors: Colgate S. O.
Published: February 2005

Design and construction details are given for a one piece, air-cooled, flange-type baffle having improved conductance characteristics.
New Double-Beam Fluorometer
Authors: Laikin Milton
Published: February 2005

The design of a new double-beam fluorometer is described. This fluorometer uses a new double-beam lamp to alternately irradiate sample and reference. The resultant fluorescent light is detected by a photomultiplier. After amplification, the sample and reference signals are separated by means of a ring demodulator. The reference signal is fed back to the photomultiplier dynode supply and the sample signal to a meter which indicates the ratio of sample to reference. Ultimate sensitivity for quinine sulfate is 1 part per billion full scale.
Theory of Plasma Wave Probes in a Collisionless Plasma
Authors: Drummond William E.
Published: February 2005

The theory of the emission of longitudinal plasma waves by a pair of grids immersed in a hot plasma is developed using the Vlasov equation. The energy radiated by these grids is derived from a variation of the Landau treatment of spatially varying waves in a collisionless plasma. The principal result is that closely spaced grids have a surprisingly high efficiency for exciting the fundamental model of the plasma.
Force on a Small Particle in the Vicinity of a Cylinder in a Homogeneous Magnetic Field
Authors: Gill S. J. , Malone C. P.
Published: February 2005

A method for producing a large measurable inhomogeneous magnetic field by imposing a uniform magnetic field upon a cylinder of magnetic material is considered. Equations are developed for the forces on a small particle due to this inhomogeneous magnetic field, and experimental observations of the forces on a suspension of small particles are described.
Heterodyne Spectral Noise Analyzer
Authors: Van Burik H. C. J. , Wessels A. C. E.
Published: February 2005

An electronic heterodyne noise analyzer has been developed with the following properties: (a) Spectral noise power can be measured at any frequency between 10 cps and 1 Mc. (b) Three interchangeable filters (1 cps and higher) are incorporated, the bandwidths of which are independent of the frequency in the whole frequency range covered. They allow for a high resolving power in the whole frequency range concerned and in addition for high accuracy at relatively short measuring times. (c) No response to harmonics of the analysis frequency is found.
Precision Capacitance-Conductance Bridge for Dielectric Measurements at Audio and Low Radio Frequencies
Authors: Mungall A. G. , Morris D.
Published: February 2005

An inductively coupled ratio arm bridge for accurate measurement of the dielectric properties of materials at frequencies from 1 to 100 kc is described. Errors in the determination of very low loss tangents dependent on stray capacitance and nonideal ratio arm characteristics are discussed, and ways of decreasing them outlined. Design and performance data for the bridge are given.
Germanium as a Neutron Monochromator
Authors: Barrett C. S. , Mueller M. H. , Heaton L.
Published: February 2005

A comparison has been made of several ways of introducing different amounts of imperfection into neutron transmission monochromators of germanium in order to control their efficiency. The recommended technique is uniaxial plastic compression along the [110] direction at 650°C to a reduction in thickness equal to or slightly under 2.5%. Tests indicate an improvement in efficiency in both single-crystal and power diffractometry of a factor of 25 to 40 over that of an undeformed slab.
Heavy Ion Energy Accumulation in the Tandem Van de Graaff Accelerator
Authors: Moak C. D. , Neiler J. H. , Schmitt H. W. , Walter F. J. , Wells G. F.
Published: February 2005

A new energy-accumulation method has been found for accelerating very small but usable beams of artificial fission fragments such as bromine and iodine ions to energies three times higher than those previously available from tandem Van de Graaff accelerators. Energies up to 120 MeV now available cover completely the energy range found for the fission particles from uranium. The ions have been used to study the behavior of silicon solid-state fission-particle detectors of many types. For the first time direct calibration methods are available to aid in experimental studies of the fission process. Further work will be directed toward an experimental study of the stopping power of various elements for heavy ions.
Method for Measuring Sonic Dislocation Velocities
Authors: Carlsson A. J. , Gilman J. J.
Published: February 2005

Explosions (lead azide) at the two ends of a crystal rod are made simultaneously (to <1/50 μsec) using exploding wires as detonators. The resulting elastic pulses meet and reinforce at the center of the bar to produce transient plastic flow, and the pulse length is short enough to allow dislocation velocities to be measured up to the transonic range.
Phosphorescence Method of Reading Thermoluminescent Dosimeters
Authors: Schulman J. H. , West E. J.
Published: February 2005

It is shown that multiple readings of thermoluminescent dosimeters can be made by using the ``steady-state'' phosphorescence brightness at a temperature well below the glow peak temperature. Following such readings the devices can be read in the normal way, with appropriate calibration factors to correct for the partial exhaustion of the phosphor by the phosphorescence readings. The behavior of dosimeters in the phosphorescence method of reading appears to be more dependent on constructional details than in the normal thermoluminescent method.
Mass Abundance Ratiometer for a Single-Beam Mass Spectrometer
Authors: Pelah I. , Dattner J. , Fischler J.
Published: February 2005

An electronic ratiometer with synchronous switching has been built, permitting the measurement of mass abundance ratios with a single-beam mass spectrometer. The ratiometer eliminates some of the drawbacks in the measurement of isotope abundance ratios with a double-beam mass spectrometer and allows mass abundance ratios differing by many mass units to be measured, giving the possibility of following the ratios of reactants and products in fast gas kinetic studies.
Automatic Magnetic Susceptibility Apparatus
Authors: Richardson J. T. , Beauxis J. O.
Published: February 2005

This paper describes a fully automatic magnetic susceptibility balance. Sample weight, magnetic weight changes, and temperature are recorded during a timed cycle, with programmed temperature regulation from −196 to 500°C. The apparatus greatly extends the convenience, range, and applicability of magnetic studies.
Improved Method for the Psychophysical Study of the Temperature Sense
Authors: Kenshalo D. R.
Published: February 2005

Peltier refrigerators are almost ideal transducers to provide the precise temperature control necessary for investigation of thermal sensitivity. The operation of Peltier refrigerators is briefly described and a circuit is presented which automatically controls the temperature of the refrigerator to within ±0.025°C of a predetermined value. Changes in the temperature of the refrigerator from 0.05 to 10°C can be obtained with less than a 2% error.
Purity of Hydrogen Permeating Through Pd, Pd-25% Ag, and Ni
Authors: Young J. R.
Published: February 2005

Hydrogen permeating Pd and Pd-25% Ag has been found to have an impurity content as low as a few parts in 1010. A technique is described that allows a determination of the impurity content in hydrogen to be made quite easily.
Model of a Mass Spectrometer which Simultaneously Collects Positive and Negative Ions
Authors: Flesch Gerald D. , Svec Harry J.
Published: February 2005

A model of a mass spectrometer which detects positive and negative ions simultaneously has been built and tested. The ion source consists of two conventional Nier-type sources arranged back to back in which the electron gun is maintained at ground potential and the ion accelerating electrodes either positive or negative with respect to ground. Positive ions are extracted in one direction and negative ions in the diametrically opposite direction. Mass separation is achieved by means of two 180° magnetic sectors with an ion trajectory radius of 1½ in. Mass resolution of approximately 1/60 has been obtained. Mass spectra are scanned magnetically. The model has served well to aid in the solution of circuit problems which will be encountered in a large model of the instrument. Results have been obtained on the mass spectra of chromyl fluoride, CrO2F2, and Freon 12, CCl2F2, which satisfy the original design objectives for the model. Some crude appearance potentials have been attempted for the observed positive and negative ions from CCl2F2.
Catheter-Tip Blood Flowmeter for Measurement of Pulmonary Arterial Blood Flow in Closed-Chest Dogs
Authors: Pieper Heinz P.
Published: February 2005

The design of a catheter-tip flowmeter attached to the end of a flexible catheter is presented. The instrument employs a differential transformer with variable coupling. Performance tests have been made which demonstrate the reliability of the instrument for measuring pulsatile flow.
Semiautomatic Modulus of Rupture Tester for Operation in Vacuum or Inert Atmospheres
Authors: Arias Alan
Published: February 2005

The construction and operation of a semiautomatic modulus of rupture tester for determining the modulus of rupture up to 2400°C in either vacuum or inert atmospheres are described. One of the unique features of the apparatus is its ability to test up to 18 specimens without being reloaded. This paper includes a description of the auxiliary equipment used in conjunction with the tester and a typical curve of modulus of rupture against temperature obtained with this tester.
Accurate Low Magnetic Field Measurements on Superconducting Coils
Authors: McEvoy J. P. , Decell R. F.
Published: February 2005

Sensitive Hall effect probes, which are now commercially available, have been used to measure the magnetic fields generated by superconducting coils. The sensitivity has been measured to be 0.080 V/kG-A at 4.2°K. Field resolution at IH=100 mA using a Keithley 149 millimicrovoltmeter is 12.5 mG. The probe calibration is linear from 0–6 kG which is the range of interest for several experiments which are described. Probe performance is demonstrated by measurements of the residual field of a NbZr solenoid, the magnetization of vapor-deposited Nb3Sn cylinders, and the uniformity of a superconducting magnet for a traveling wave maser.
Null-Reading Microbalance and its Use in the Study of the Infrared Spectra of Adsorbed Molecules
Authors: Seanor D. A. , Amberg C. H.
Published: February 2005

A null-reading quartz spring microbalance is described which has been designed to measure the weight of gas adsorbed on thin pressed wafers suitable for infrared transmission studies. Its operation, calibration, and precision are discussed and special reference is made to the determination of integrated intensities of the infrared absorption bands of surface species.
Tunneling Current Structure Resolution by Differentiation
Authors: Thomas D. E. , Klein J. M.
Published: February 2005

Structure in the current-voltage characteristics of heavily doped p-n junctions and superconductor junctions is more clearly revealed if the current is differentiated with respect to the voltage and is still more clearly revealed if a second differentiation is performed to obtain d2I/dV2. This paper describes a working system for automatically measuring and continuously plotting these derivatives as a function of voltage. Traces of current-voltage characteristics of heavily doped degenerate p-n junctions and the first and second derivatives of these characteristics obtained by the techniques described are given. A series of first derivative curves for an Al-Al2O3-Pb tunnel junction is also included to illustrate the speed of the method.
Ion Source for Low-Energy Collision Studies
Authors: Vance Dennis W. , Bailey T. L.
Published: February 2005

An ion source is described which produces either positive or negative ion beams by electron bombardment of a jet of gas at relatively high pressure. The electrons are confined to an ionization region by a reflection-collimation geometry. The ion currents produced are moderate (∼10−9 A) but the ion beams are very stable and noise-free, and have a small spread in kinetic energy as required for low energy collision studies. Most of the data presented pertains to negative ions, although some positive ion results are given.
Nanosecond Scintillation Coincidence Spectrometer System with High Reliability
Authors: Beller L. S.
Published: February 2005

A low-energy scintillation coincidence system capable of few-nanosecond resolution and very low timing jitter is described. Saturating circuit techniques are used to make the performance nearly independent of tube parameters, resulting in stable and reliable performance over periods of months.
New Instrument for Measuring Evaporation; Application to Evaporation of Water through Thin Films
Authors: Walker Donald C.
Published: February 2005

A new instrument quickly and accurately determines evaporation rates of water. A probe passes helium over a small area of the water surface; the vapor picked up by the helium returns through the probe and is continuously measured by a thermal conductivity cell. Accuracy and repeatability are within 1% absolute. The apparatus is sensitive to a change in evaporation rate of less than 1%; response is 5 to 20 sec, depending upon the magnitude of the step change. The instrument, called an evaporometer, is especially useful for rapidly screening water-evaporation retardants and for determining evaporation rates through monomolecular films spread on the water surface of the film balance. Evaporation rate vs film pressure isotherms, determined simultaneously with pressure vs area isotherms, should yield additional information about the composition and structure of the monolayers. Although the evaporometer was developed for the determination of water evaporation, it is adaptable to nonaqueous liquids.
Sensitive Tritium Counting with a Propane Proportional Counting System
Authors: Eulitz G. W.
Published: February 2005

Comparison of the minimum detectable amount of tritium by different counting devices shows that proportional gas counting is the most sensitive method at the present time. A new method of tritium proportional gas counting using propane as counting gas is described. The propane is formed by hydrogenation of propyne with palladium oxide as a catalyst. Using a 2.5-liter counter filled with propane at 2.2 atm pressure requires a sample size of half a mole of H2O or H2. For a background of 5.3 cpm, this results in a minimum detectable concentration, without isotopic enrichment of tritium, of 3 TU equal to ±2σ for a counting time of 1000 min.
Particle Size Classifier for the Subsieve Range
Authors: Burson John H. , Iinoya Koichi , Orr Clyde
Published: February 2005

A particle size classifier for dry powders in aerosol form, based on the combined classifying mechanisms of impaction, adhesion, and the characteristic trajectories of particles, has been developed and extensively tested with a variety of powders. Continuous classification has been achieved for powders the diameters of which are predominantly below 50 μ by impacting the aerosol cloud onto a moving surface and recovering those fractions resulting from the aforementioned mechanisms. Partial separation of powder mixtures is sometimes possible when the components have widely differing physical properties.
Pressure Measurements Below 10−10 Torr with Bayard-Alpert and Magnetron Gauges
Authors: Torney Franklin L. , Feakes Frank
Published: February 2005

Below 1×10−10 Torr, pressure measurement by means of Bayard-Alpert type ion gauges is complicated by the existence of a current associated with soft ``x-rays.'' The precise measurement of a true ion current requires precise determination of the so-called x-ray limit of each gauge. The present work describes the use of a Bayard-Alpert gauge containing a modulating electrode (after the design of Redhead) to measure pressures below 10−10 Torr. Magnetron-type gauges, which do not have x-ray limitations, were then compared directly with the Bayard-Alpert gauges. In addition, gauge comparisons were carried out in a dynamic system involving pressure ratios across a capillary. Both series of experiments showed that the output current of the magnetron gauge was a power function (exponent 1.6) below approximately 2×10−10 Torr (N2). In the latter work it was possible to make measurements to below 1×10−12 Torr N2 equivalent.
Use of an Analog-to-Digital Converter in Pulsed Nuclear Resonance
Authors: Stejskal E. O.
Published: February 2005

The use, in pulsed nuclear resonance experiments, of a voltage-to-frequency converter and an electronic counter to act as an integrator for the observed signals is described. Because measurements of this type are free of most subjective influences, they improve upon continued replication. Data are obtainable in a form which may easily be processed by a digital computer. Increased accuracy and sensitivity are the result. Sample T1 determinations are presented. The relaxation in a sample showing a single T1 is followed to within one part in 104 of equilibrium. Remarks are made concerning the design and use of a calibration equation capable of accounting for the behavior of a vacuum tube diode detector biased for linear operation.
Simple Transistorized Logarithmic Time Base
Authors: Idnurm M.
Published: February 2005

A time base is described which allows the spot of a cathode ray tube to be deflected at a rate proportional to the logarithm of the time. The circuit requires the use of two transistors, one of which serves as a conversion stage and the other as an amplifier stage. Two different sets of component values are given to cover a range of either two or three decades. The performance of the time base and its limitations in respect to temperature variations and supply voltage fluctuations are discussed.
Photodiode as a Sensitive Temperature Probe
Authors: Dimick R. C. , Trezek G. J.
Published: February 2005

A temperature probe capable of reading temperature deviations of ±0.005°F or less at ambient temperatures has been developed using the large temperature coefficient of the reverse current of a Sylvania 1N77B photodiode. The photodiode case, a 0.072-in.-diam×0.80-in.-long glass cylinder, makes possible a small but very rugged probe assembly.
Liquid-Helium Temperature Regulator
Authors: Blake C. , Chase C. E.
Published: February 2005

An electronic regulator is described that is capable of controlling the temperature of a liquid-helium bath within ±10 μdeg for a few minutes and reducing long-term drift to less than 40 μdeg/h. With occasional adjustment, the temperature can be indefinitely maintained within ±10 μdeg. The circuit is designed to be used with a resistance thermometer bridge previously described. The error signal from the bridge is displayed on a meter, so that the bridge can be balanced without use of an oscilloscope and the performance of the regulator can be continuously monitored.
Two-Component Microbalance for Measuring the Forces on Ion-Bombarded Surfaces
Authors: Rogallo Vernon L. , Savage Howard F.
Published: February 2005

A two-component null-type microbalance has been developed to measure forces due to ion bombardment on a surface. The balance employs the principle of the attracted disk electrometer. The sensitivity can be adjusted by simply changing the location of the center of gravity. Measurements of a few micrograms of force in two perpendicular directions can be made simultaneously.
Optical Cells for the Observation of Raman Scattering in Gases at Medium Pressures
Authors: May A. D. , Stryland J. C.
Published: February 2005

Recent investigations of the broadening and shift of isotropic Raman lines of compressed hydrogen have demonstrated the effects of intermolecular forces on intramolecular motions. This paper describes two cells suitable for such experiments in the low to medium density range. The first is a cell for use at 85°K and 100 atm, which is similar in design to a conventional Raman source. The second cell, for use at room temperature and at pressures up to 1000 atm, utilizes the large compressive strength of glass and is an improved version of a cell reported previously. High resolution Raman spectra of the Q1 branch of hydrogen have been obtained in the range 25 to 400 times standard density both at liquid air and room temperature.
Photomultiplier Gain Stabilization Circuit
Authors: Ageno M. , Felici C.
Published: February 2005

A simple method is described for the gain stabilization of a photomultiplier in which the stabilization system does not interfere with the fast pulse spectrum to be measured. The functioning principle consists in sending a low frequency (77 Hz) and very low intensity light pulse, which gives a modulation of the photomultiplier thermionic noise, on the photocathode together with the scintillation light. The modulation frequency is then selected on the anode by a special filter. The signal obtained in this way is used to trigger a feedback circuit, which makes the photomultiplier gain constant by suitably varying its voltage.
Chemisorption Detector for Oxygen
Authors: Collins Donald J. , Hoenig Stuart A.
Published: February 2005

A chemisorption detector for oxygen has been developed. The device depends upon the increase in work function of a tungsten filament when chemisorption of oxygen occurs. The device is sufficiently sensitive to detect oxygen at pressures of 10−11 Torr and is insensitive to nitrogen for ratios of nitrogen to oxygen as high as N2/O2≈10/1.
Continuous Zone-Refining Apparatus
Authors: Kennedy John K.
Published: February 2005

A continuous zone-refining system is described wherein matter transport is used as a means of producing material flow in one of the two sections of the system. This system provides more rigid control of operational parameters by increasing the planarity of solid-liquid interfaces and the reproducibility of the product flow per pass. Use of the matter transport phenomenon increases the flexibility of design of a zone-refining system which can result in increased purity of the product. Equations describing the system are reported.
Apparatus for X-Ray Measurements at Very High Pressure
Authors: Perez—Albuerne E. A. , Forsgren K. F. , Drickamer H. G.
Published: February 2005

An apparatus has been developed which permits x-ray powder patterns to be obtained to over 500 kilobars presure. The apparatus is derived in part from the supported tapered piston electrical resistance apparatus in use in this laboratory, but the x rays are transmitted through a thin layer of LiH with suitable platinum collimation. The pressures are established by measuring the change of lattice parameter of a suitable marker mixed with the sample. These changes are then compared with volume changes obtained in shock wave work. Usual markers used to date include silver, rhodium, and palladium. Typical data for sample pressure versus average applied pressure for these metals are given. Also included is the change in lattice parameter with pressure for CsCl to 500 kilobars. The results are compared with the extrapolation of Bridgman's data.
Improved Quiescent Plasma Source
Authors: Rynn Nathan
Published: February 2005

The present day version of a source of low temperature, fully ionized, quiescent plasma, known as the Q-1 device, is described. A simplified form of the theory is presented and is extended to include absorption at the walls. The many modifications and improvements that have been made since the device was first built are described.
Liquid Nitrogen Cryostat to Facilitate Isothermal Annealing Studies on Metals after Heavy-Particle Bombardment
Authors: Dworschak F. , Herschbach K. , Witt F. E. L.
Published: February 2005

A cryostat is described which has been developed for irradiating a number of small metal specimens with a high beam current of heavy particles at liquid nitrogen temperature. The specimens, which are mounted on a block, are taken out of the cryostat after irradiation and subsequently annealed in a temperature bath. The progress of annealing is followed by measuring the change in electrical resistivity of the specimens in liquid helium.
Gamma-Ray Circular Polarization Analyzer Using a Rapidly Alternating Magnetic Field
Authors: Pechacek Robert E. , Mann Lloyd G. , Bloom Stewart D. , Rodrigues Richard M.
Published: February 2005

Gamma rays from substances with half-lives approaching 0.1 sec may be analyzed using a magnet whose saturated field reverses in 0.4 msec. Laminated magnetic material and transistor circuitry are used to achieve the fast field reversal. The magnet consists of 4-mil Supermendur tape wound on a toroidal core. The high permeability and low loss of this material permits it to be driven by a single turn at reasonable currents. The circuit uses a low voltage, high current power supply, and charging inductors to provide the necessary voltage pluses. These pulses are developed across switches consisting of ten 2N1358 power transistors operated in parallel. The system has operated 2000 h without a failure.
Modes of Operation of an Electron Beam Floating Zone Melting Furnace: Growth of Single Crystals of Metals and Alloys
Authors: Sell Heinz G. , Grimes Willard M.
Published: February 2005

An electron beam melting furnace constitutes a dynamic high vacuum diode which has theoretically six modes of power regulation as a consequence of the current-voltage characteristic of the furnace and the choice between constant-current or constant-voltage control. Among the six possible modes, three are unstable and three are useful. Preference is given to constant-current control as this is more efficient than constant-voltage control and has the added advantage of an electrothermal feedback loop which increases the stability of regulation. A single tube constant-current regulator is described which utilizes tungsten filament lamps in the feedback loop. This regulator was incorporated in the power system of an electron beam melting furance. Numerous single crystals of tungsten, other metals, and alloys were grown. The performance of the furnace and the quality of the crystals are discussed.
Energy Distribution of Ions Formed in the rf Spark Source
Authors: Woolston J. R. , Honig R. E.
Published: February 2005

Utilizing the ion source and electrostatic analyzer of a double-focusing mass spectrograph, the energy distribution of the ions formed by the pulsed rf vacuum spark has been determined for various materials and sparking conditions. Upon emerging from the electrostatic analyzer, the ion beam has a width, in the y direction, which is principally due to its angular divergence α and its energy spread β. By suitably reducing the widths of the defining slits, α can be made negligibly small. The beam width is then a nearly linear function of β alone, and a photoplate, placed just beyond the exit of the electrostatic analyzer, is used to determine the energy distribution of the ions produced in the source. A convenient energy scale is put on the same photoplate by exposing it to thermal ions (energy spread about 0.5 eV) which are accelerated to selected voltages while the deflecting voltage in the electrostatic analyzer is kept constant. In the present study, a 1×2 in. photoplate could be shifted by external means to permit 31 exposures to be made. Thus, many different sparking conditions and electrode materials, together with thermal ion calibrations, could be investigated and compared in a single experiment. At an accelerating voltage of 20 kV, an energy range of more than 3000 eV is recorded. The residual α, set by two 0.001-in. defining slits, permits an energy resolution of 15 eV. The energy distribution of the ions produced by the rf spark depends strongly on the spark-gap width, the rf voltage, and the electrode material. The narrowest energy spread possible is obtained with metallic electrodes at small rf voltages. So far, only two special cases were found where 90% of the ions were contained in an energy band no more than 500 eV wide. In all other instances, energy spreads are found to range from about 1000 to perhaps 5000 eV, with the mean energy located up to 1300 eV above the accelerating voltage. The fine structure and significance of these distributions is discussed in some detail.
Adaptation of an X-Ray Diffractometer for Thin Film Studies by Total Reflection of X Rays
Authors: Mozzi R. L. , Guentert O. J.
Published: February 2005

In studying solid surfaces by the total reflection of x rays it is important to use monochromatic radiation with a narrow angular divergence and to employ a mechanism for precisely aligning the surface of the sample relative to the incident beam. An x-ray monochromator, based on the phenomenon of anomalous transmission in nearly perfect germanium crystals, and a sample holder are described which convert a conventional x-ray diffractometer to an x-ray reflectometer without altering its basic design. Procedures for alignment and operation of the reflectometer and a sample measurement of the thickness and density of a thin titanium film are presented.
System for Continuous Generation and Fast Transfer of Radioactive Gases
Authors: Pleasonton Frances , Johnson C. H.
Published: February 2005

The system was developed to provide a stable and strong source of He6 for the Oak Ridge National Laboratory recoil spectrometer. A continuous flow of water-vapor swept the He6 through about 80 ft of piping from the generator to the laboratory in 3 to 4 sec; the gas was then purified and delivered to the spectrometer in an additional 1 to 1.5 sec. Modifications in design for other experiments and for use in leak detecting are discussed.
Large Volume Scintillation Chamber for Radon Counting
Authors: Kraner Hobart W. , Schroeder Gerald L. , Lewis Anthony R. , Evans Robley D.
Published: February 2005

A 450-cc cylindrical Lucite chamber covered internally with ZnS(Ag) and viewed at each end by 5-in. photo-multiplier tubes with summed outputs has been used routinely as a low background (∼0.8 counts per min for a new chamber) Rn scintillation counter. The counter is simple to construct and has operated reliably for about two years. The counting efficiency for Rn in transient equilibrium with its two alpha-emitting daughters is 2.1 counts per Rn decay. Thin lines of silver conducting paint applied externally on the ends of the chamber, together with surrounding Al foil, form a complete electrostatic shield which has assured reproducible counting efficiencies by suppressing randomly occurring internal fields. Results of experiments, in which external potentials were applied to the end plate electrodes of an experimental chamber, are presented in detail. It was found that as little as 22 V applied across the chamber can change the counting efficiency by 8%. A back voltage effect caused by the deposition of ionization-induced charge on the internal surfaces during voltage application was observed.
Simple Partial Pressure Gauge
Authors: Goldstone L.
Published: February 2005

A gauge based on the 180° mass spectrometer is described which is simple to make and to operate. It can be used to analyze the constituent gases in a vacuum system at partial pressures as low as 2×10−11 Torr. Several of these instruments have been tested and the sensitivity and resolution have been constant to within 10%. The gauge has a resolution of about 50, which is adequate for separating the common residual gases in a high vacuum system, and it is small so that it can easily be outgassed. Constructional details are given, and its operating characteristics are discussed.
Use of Electrochemiluminescence in the Measurement of Mass Transfer Rates
Authors: Springer George S.
Published: February 2005

When a potential is applied between two platinum electrodes immersed in a flowing chemiluminescent solution, a blue glow appears at the surface of the anode. An electrochemical system suitable for generating the glow is described. Experimental results are presented showing the effects of the parameters on the intensity of the glow. It is shown that for a given potential and a given solution the light intensity is governed solely by mass transfer of the chemiluminescent substance to the surface of the anode.