bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability and Calibration of Miniature Platinum Resistance Thermometers
Authors: Johnston W. V. , Lindberg G. W.
Published: February 2004

Miniature platinum resistance thermometers have been evaluated for use as substitutes for the capsule type resistance thermometer in which smaller size but comparable precision and accuracy are required. The thermometers tested weigh about 1 g. The thermometers were calibrated between 12 and 373 K at fixed points and by comparison with an N.B.S. calibrated capsule type platinum resistance thermometer. The values obtained for the fundamental constants (α,β,δ) of the Callendar-Van Dusen equation meet the requirements of the International Practical Temperature Scale above 90 K. At temperatures below 90 K, the RT/R273.15K drops less rapidly than for the capsule type thermometers, indicating a possible geometrically caused strain in the platinum. Because of this difference, it was not possible to interpolate between measured points by deviation plots in the manner ordinarily used when calibrating thermometers below 90 K. It was found that by using the data points as a basis for Lagrange's interpolation polynomials, a table could be generated that fit a smooth curve through the data to better than 0.002 K. Over a 12 month period the R0 of the miniature thermometers have been reproducible to 10 ppm.
Tensile Loading Device for Kossel Microdiffraction and Metallography
Authors: Vieth D. L. , Yakowitz H.
Published: February 2004

A loading device used primarily in conjunction with Kossel (divergent beam) x-ray diffraction is described. The device is compatible with any standard upright metallograph as well. It is 10.1 cm in diameter and accommodates specimens 2.5 cm in reduced section by 6 mm wide. The device utilizes small load cells having ranges of 0 to 44.5 N and 0 to 445 N respectively. Load cell error is ±0.5% of the full load capacity. Load changes of 0.2% of load capacity can be observed. The load device is mechanically and electrically stable. Loads are read on a standard commercial universal indicator.
New Type of Monovelocity Electron Source
Authors: Marmet Paul
Published: February 2004

A new instrument is calculated which makes possible the transformations of an electron beam of wide energy spread into an intense monovelocity beam suitable for electron impact work. In this paper, only the most promising models are calculated and the predicted results raise the possibility of producing intense beams of monovelocity electrons in a nonfield-free region, consequently reducing noise and secondary reactions.
Faraday Balance for Measuring Magnetic Susceptibility
Authors: Morris Bernard L. , Wold Aaron
Published: February 2004

An apparatus for measuring magnetic susceptibility by the Faraday method is described. It is capable of measuring susceptibilities ranging from 0.01×10−6 to 500×10−6 emu/g over a temperature range of 5 to 300 K, in fields up to 10 kOe, with a precision of 0.2% and an accuracy of 1%. Various problems associated with the measurements, such as thermomolecular flow, ferromagnetic impurities, and electrostatic forces, are discussed It is shown that problems arising from thermomolecular flow can be avoided by controlling the pressure of exchange gas. Correction for ferromagnetic impurities involves extrapolating the susceptibility vs 1/H to infinite field. Several methods for minimizing the problems caused by electrostatic force are discussed. The versatility of the balance is demonstrated by measurements made on NiTiO3 (χmax=229×10−6 emu/g) and K0.3 MoO3 (χ≈0.06×10−6 emu/g).
Cryostat for the Measurement of Thermal Conductivity and Specific Heat between 0.05 and 2°K
Authors: Harrison J. P.
Published: February 2004

A cryostat is described which is capable of measuring specific heat and thermal conductivity of dielectric crystals over the temperature range 0.05 and 2.0°K. Thermal conductivity is measured with a steady flow of heat through the sample, and specific heat by a pulse technique. Differential carbon resistance thermometry is used for both measurements. The performance is demonstrated on the thermal conductivity of LiF, and on the specific heat of two samples of nominally pure KCl.
Pneumatically Operated Microelectrode Puller for Use in Electrophysiology
Authors: Lab Max J. , Maddison W. C.
Published: February 2004

Micropipettes suitable for intracellular use are pulled by a vacuum applied to the nozzles of two glass syringes. The ends of the glass tube are attached to the plungers, which are pulled home in opposite directions. The two pulls are in a straight line and can be varied in velocity and duration, producing microelectrodes of different shapes and sizes. The details of construction and operation are described.
Wide-Range Pulse-Shape Discrimination System
Authors: Hollandsworth C. E. , Bucher W. P.
Published: February 2004

A pulse-shape discrimination system for use with organic scintillators is described which is based upon the true zero-crossing detection of single delay-line shaped pulses. Results of performance tests are presented in the form of contour diagrams which show the crossover-time spectra of neutron and gamma-ray induced events as a function of pulse amplitude. A technique to compensate for the variation of scintillation pulse shape with recoil-proton energy is described. Good gamma-ray rejection with nearly 100% recoil-proton acceptance over a dynamic range of 100 is obtained.
A Flying-Spot Scanner
Authors: Potter C. N. , Sawyer D. E.
Published: February 2004

A flying-spot scanner used to study the electrical properties of semiconductor materials and devices is described. The instrument automatically deflects a collimated light beam in a raster pattern and focuses the raster on the photosensitive semiconductor surface. The electrical output from the semiconductor is amplified and used to form an image of the photoresponse of the sample on a cathode ray tube. The resolution of the system referred to the sample is about 5 μ.
A Pulse-Height Analyzer for Charged-Particle Spectroscopy on the Lunar Surface
Authors: Harrington T. M. , Marshall J. H.
Published: February 2004

The design and performance of a charge-sensitive amplifier and a 256-channel pulse-height analyzer for use in a lunar surface analysis experiment are presented. Input is from silicon detectors used to measure the energies of up to 7 MeV alpha particles and protons. Anticoincidence logic is provided for the proton detection system to reject cosmic rays. The instrument operates in the space environment over a temperature range of −50 to +50°C. Over this range the instrument gain was stable to ±0.4%, and the offset varied less than 0.1 channels. Resolution of 35 keV was obtained with a 228Th alpha-particle source. Total power for the system, which includes 10 amplifiers, 2 analog-to-digital converters, 4 discriminators, and data processing logic is approximately 2 W. Particular attention was given to reliability in the design and construction of the system. Large amounts of negative feedback and carefully selected and screened components were utilized to achieve this goal.
Inductance Thermometer
Authors: Willens R. H. , Buehler E. , Nesbitt E. A.
Published: February 2004

Inductors with a large temperature coefficient of inductance have been fabricated with alloys which, as a result of rapid quenching from the liquid state, have new and unusual magnetic properties. These inductors have been incorporated in an oscillator which generates a frequency that depends upon temperature. The rate of frequency change with temperature, between room temperature and 1°K, is large enough to permit very accurate temperature measurements. The conversion of temperature to frequency makes possible easy transmission over long distances.
Null Pressure Optical Cell for Measurements on Liquids at Elevated Temperatures and Pressures
Authors: Gruen D. M. , Newman D. S. , McBeth R. L.
Published: February 2004

An optical cell used in obtaining absorption spectra at temperatures up to 500°C and pressures up to 2100 kg cm−2 is described. The cell can be characterized as a ``null-pressure'' device. The solution is contained in a sealed quartz cuvette and the pressure exerted by the solution within the cell is balanced by an external pressure of argon gas. The near ir spectra of water below and above the critical temperature are presented.
Spectrothermal Emission Aerosol Particle Analyzer (SEAPA)
Authors: Crider Walter L.
Published: February 2004

An instrument that selectively counts, according to size, aerosol particles containing certain specific metals is described. The technique employed is based on the principle of spectrothermal emission of individual particles passing through the combustion zone of a hydrogen-air flame. After the flash of light from each emitting particle passes through a monochromator, it is converted to a voltage pulse which is electronically counted according to height. The instrument sensitivity was determined for aerosols of NaCl, CaCl, CaO, Fe2O3, KOH, LiOH, MnO2, and MgO. The minimum size particle detectable varied from 0.10μ diam for NaCl to 1.22μ diam for MgO.
Fast Response Magnetometer Using Ferromagnetic Resonance in Thin Films
Authors: Schwee L. J. , Irons H. R.
Published: February 2004

A magnetometer of simple construction is described having a response time of the order of 4 nsec. In this instrument the impedance of a thin film biased near ferromagnetic resonance is a measure of the external field. At resonance the element may be matched to a transmission line. The voltage amplitude of the reflected wave varies linearly with change in the external magnetic field.
New Ionization Chamber Technique for the Measurement of Environmental Radiation
Authors: Shamos M. H. , Liboff A. R.
Published: February 2004

It is shown, contrary to usual low-level ion chamber practice, that there are unique advantages to using highly electronegative filling gases, which enhance columnar recombination. Indeed, through the proper choice of gas and electric field strength, it is possible to discriminate almost completely against alphas originating in the walls without affecting the collection of beta- and gamma-induced ionization. A number of chambers utilizing this technique have been constructed. The resulting characteristics, as well as comparisons with calibrated sources, indicate a complete absence of residual currents from wall contaminants. The fluctuations in background measurements are reduced by at least a factor of 3 over comparable air chambers.
Production of Quiescent Discharge with High Electron Temperatures
Authors: Lisitano G. , Ellis R. A. , Hooke W. M. , Stix T. H.
Published: February 2004

Collision-free quiescent plasmas are produced in a magnetic mirror geometry by applying ∼50 W uhf power to a novel coupling structure which surrounds one section of the plasma. The plasma characteristics are favorable for studies of waves, diffusion, stability, and turbulence.
Scintillomicroscope for Radioactive Tracer Detection
Authors: Reynolds George T.
Published: February 2004

An image intensifier-microscope system is described that is capable of viewing the spatial distribution of weak radioactive tracer deposits in biological specimens. The radioactive decay products are located by means of the light they emit from thin scintillators placed over the specimen. Comparisons are made with conventional autoradiographic techniques. An analysis is given of the sensitivity of the system. Results obtained from the application of the technique to 14C detection in Schistosoma mansoni are presented and discussed.
Automatic Recording of Liquid Surface Tension
Authors: Smith Tennyson , Schlein H.
Published: February 2004

A simple system is described that records directly the surface tension of any fluid by averaging the differential pressure of bubbles forced simultaneously from two tubes having the appropriate dimensions and geometry. This system records the value of the surface tension with a 2% error. A more complex system is described that records directly the surface tension of any fluid by measuring the difference between the maximum pressure to force bubbles from one tube with respect to another. This system records the value of the surface tension with an error of ≤0.3%.
Mechanical and Piezoelectric Properties of Shock-Loaded X-Cut Quartz at 573°K
Authors: Rohde R. W. , Jones O. E.
Published: February 2004

The mechanical and piezoelectric properties of uniaxially strained X-cut quartz were studied at 573°K over a stress range of 6 to 21 kilobars by monitoring the current output from a shock-loaded quartz disk. In addition to providing fundamental knowledge of the behavior of quartz under these conditions, the results yield data necessary for the application of quartz as a submicrosecond stress gauge at this temperature. The elastic wave velocity was found to be 5.70 mm/μsec at 573°K, a 0.35% decrease from the room temperature value. The piezoelectric factor relating the piezoelectric charge to stress was determined as k = (1.895×10−8+1.470×10−10σx) C/(kilobar-cm2). This value is based on room temperature values of the electrode area and the gauge thickness. In the zero stress limit, the piezoelectric factor determined by shock loading compares favorably with the e11/c11 piezoelectric coefficient of quartz. Above 14 kilobars, relaxation in the current output of the quartz was observed. Therefore, when using quartz as a gauge at 573°K at higher stresses, some caution must be exercised in interpreting the entire stress-time history recorded. This relaxation in current does not affect the precision of the quartz gauge for the measurement of step-input stresses. One experiment performed at 17 kilobars and 743°K indicates the usefulness of the quartz gauge at this temperature.
Photometer for Measurement of the Light Scattered by Large Submicron Cylinders at Both Perpendicular and Oblique Incidence
Authors: Cooke D. , Kerker M.
Published: February 2004

A light scattering photometer is described which is capable of viewing the periphery of the cone of light scattered by a cylinder tilted obliquely to the incident beam. The special case of perpendicular incidence can also be handled. Experimental data with a Pyrex cylinder show excellent concordance with theoretical calculations for a cylinder with a diameter of 525 mμ.
Use of an Impedance Comparator as a Fast-Balancing Alternating-Current Bridge
Authors: Solomons C. , Berg R. E.
Published: February 2004

A commercial impedance comparator is modified to permit its use as a fast-balancing ac bridge (in, for example, electrolyte resistance studies) without interference from the out-of-balance overload protection circuit. Instead of needing a slow, trial-and-error preliminary adjustment to within about ±15% of balance, the bridge may be balanced rapidly by visual indication even from a ratio of zero: infinity.
Optical Lever Technique Adapted to Hypervelocity Impact Experiments
Authors: Gregson Victor G.
Published: February 2004

An optical lever technique is adapted to hypervelocity impact experiments. The technique permits shock velocities and free-surface rotations to be measured by a general relation valid at any shock incidence angle, as well as an off-axis impact. The technique uses seven double-pulsed xenon flash tubes and a small aperture, continuously rotating streak camera. Photographs of streak camera records from impact experiments in 2024-T4 aluminum illustrate the technique.
Source of Polarized Lithium and Cesium Ions
Authors: Miers R. E. , Anderson L. W.
Published: February 2004

A source for polarized Li+, Li++, Cs+, Cs++, and Cs+++ ions is described. The ions are produced by electron bombardment of polarized Li0 or Cs0 atoms. The ion currents obtained are 3.3×10−8 A Li+, 1.3×10−9 A Li++, 6.0×10−8 A Cs+++, 1.4×10−7 A Cs++, and 6.6×10−7 A Cs+. The background current of these ions is negligible. The polarization of the ions was not measured, but a discussion of the polarization is presented. This discussion leads to the conclusion that the nuclear vector polarization of 7Li+ is about 25% and the electronic polarization of 7Li++ is about 9.4%. Possible applications of the Li++ and Cs++ beams are discussed. An interesting result from this work is the average cross section for incident electrons of 200 to 325 eV energy for the process e−+Li0 → Li+++3e−, which has the value 3.5×10−18 cm2.
Modification of a Time-of-Flight Mass Spectrometer for Investigation of Ion-Molecule Reactions at Elevated Pressures
Authors: Futrell Jean H. , Tiernan Thomas O. , Abramson Fred P. , Miller C. Dean
Published: February 2004

Extensive modifications of a Bendix time-of-flight mass spectrometer have been accomplished to permit investigation of ion-molecule reactions at ion source pressures up to about 1 Torr. In contrast with previous attempts to operate a TOF mass spectrometer, the present method employs a continuous electron beam and a dc extraction field in an ion source similar to those used in magnetic mass spectrometers. The master pulse initiating the timing cycle for mass analysis is applied to a focus grid in the low pressure region external to the source chamber and an auxiliary positive blocking pulse is applied to limit the sampling region during the ``on'' cycle. This modification eliminates degradation of instrument performance resulting from charge exchange and other secondary processes during ion acceleration, thereby extending the pressure range over which the ion source is operable by about two orders of magnitude and simultaneously increasing significantly resolution at moderate pressures. Additionally, a novel dual-inlet sample handling system which monitors directly and controls ion source pressure is described. Details of source design and performance are given, and it is demonstrated that kinetic data obtained using this system are in good agreement with previous results.
Vector Plotting Display
Authors: Churchill M. J.
Published: February 2004

A device for recording phase detected signals in vector form as a function of time or position is described. Picture records obtained by using this device to display signals from a nondestructive eddy current tester as a function of position on a sample are included.
Differential Microcalorimeter for Biochemical Reaction Studies
Authors: Berger Robert L. , Chick Yu-Bing Fok , Davids Norman
Published: February 2004

A differential solution microcalorimeter with a mixing system is described. Up to 1 ml of reagent A may be mixed with up to 3 ml of reagent B in less than 1 sec with a heating artifact of less than 0.5 mcal. A temperature range of 0 to 40°C has been utilized with a 2 h temperature equilibration time. The time course of biochemical reactions has been followed for up to 1 h. Computer simulation of the calorimeter permits data correction for heat conduction losses. For reaction heats greater than 25 mcal, ΔH and the rate constant of the reaction may be determined to ±2%. Detectivity is ±20 μcal. A digital computer simulation technique based on a finite-element analysis of heat conduction, which is of general applicability, was developed to correct the output data for heat conduction losses.
Light Source Control System for Electroreflectance Studies on Semiconductors
Authors: Williams E. W. , Parham D. V.
Published: February 2004

A feedback source-control system has been designed for electroreflectance measurements on semiconductors. An amplified dc off-balance voltage is used to control the light source and compensate for the wavelength variation of the various optical components. The percentage modulated reflectance was therefore measured directly over the experimental wavelength range. The system was applied to infrared measurements of the fundamental edge of GaAs and (Ga, In)As in the wavelength range 8000 to 11 000 Å. The extension of this system to other experiments is discussed.
Detection of Strong Shock Waves with Plastic Tapes
Authors: Champion A. R. , Benedick W. B.
Published: February 2004

A simple and inexpensive method for detecting the arrival of a strong shock wave at a surface is described. A thin layer of plastic tape produces a short duration current pulse when subjected to a plane shock wave. When a layer of plastic tape approximately 0.1 mm thick is fastened between an aluminum plate and a copper electrode, a 150 kilobar shock wave propagating from the aluminum into the tape produces a 10 V pulse across a 50 Ω load from an electroded area of 1.25 cm2.
A Ferromagnetic Resonance Method of Measuring Magnetostriction Constants
Authors: Smith A. B.
Published: February 2004

A new method of measuring magnetostriction constants in cubic ferromagnetic insulators has been developed and applied to the measurement of certain ferrites and garnets. This method utilizes the fact that the ferromagnetic resonance frequency is stress dependent. Since the magnitude of this stress dependence is determined by the magnetoelastic constants of the material, these constants can be determined by measuring resonance frequency changes induced by known stresses. One of the advantages of this method is that conventional ferromagnetic resonance measurements of the anisotropy constants, g factor, and linewidth can be made simultaneously with the magnetoelastic-constant measurements.
Mass-Energy Spectrometer for Space Plasmas
Authors: Ogilvie K. W. , McIlwraith N. , Wilkerson T. D.
Published: February 2004

A satellite-borne instrument for the study of the interplanetary medium is described in detail. This plasma experiment illustrates a whole class of such measurements that can now be done on small unmanned scientific satellites. Plasma ions are resolved in both energy and mass per unit charge in order to determine hydrogen-helium abundance ratio, ion temperatures in the ``solar wind'' and transition region, and the angular distributions and fluctuations of ion flux. Protons and alpha particles with energy per unit charge between 300 and 5000 eV are resolved to better than 5 in 103 and their energy spectrum determined. Instead of current measurements, we employ single ion counting with an efficiency of 75% at rates up to 3×107 sec−1. A histogram of counts against angular rotation is formed with a quantization of 23° and its area, variance and the azimuthal position of the peak derived by a small computer for transmission to the earth over a data link with a capacity of approximately 6 bits sec−1. Provision is made for a preliminary study of variations in the ion flux with periods greater than a few seconds. Two companion papers present the details of developments which proved necessary for this experiment and are of wider interest as well.
Crossed Field Velocity Selector
Authors: Ogilvie K. W. , Kittredge R. I. , Wilkerson T. D.
Published: February 2004

The paths of particles passing through crossed fields are calculated, with special application to the case where the particle does not complete a cycloidal oscillation. The use of such crossed fields in velocity selectors for space flight and in the laboratory is discussed. Curves are given which help in the choice of parameters for such applications.
Tunnel Diode-Transistor Binary Scaler
Authors: Tan Z. C. , Maxwell P. C.
Published: February 2004

This paper describes a new type of tunnel diode-transistor binary scaler which is very simple in concept and in design. It is capable of operating reliably at input pulse repetition rates in excess of 200 MHz. A significant feature of the scaler is that there is no maximum input pulse width restriction. Input and output circuits which allow the scaler to operate over a wide range of input driving conditions and to be cascaded directly with similar scalers are also presented.
NQR Spectrometer Using Field Effect Transistors
Authors: Viswanathan T. Lakshmi , Viswanathan T. R. , Sane K. V.
Published: February 2004

The advantages of using field-effect transistors (FET) for NQR spectrometer design are discussed. An experimental method of evaluating the performance of different oscillator configurations and optimizing the circuit parameters for best sensitivity is outlined. An NQR spectrometer system is described.
Four-Electrode Null Techniques for Impedance Measurement with High Resolution
Authors: Schwan Herman P. , Ferris Clifford D.
Published: February 2004

At low frequencies, the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization. This problem at the electrode-sample interface arises from the modulation of the normal dc boundary potential by the passage of alternating current. A solution, permitting a conductance resolution of 1:105 for frequencies between 10 cps and 1 kc, is to use a second noncurrent-carrying pair of electrodes to measure the voltage across the sample and to employ a null technique for obtaining the required precision. Several four-electrode null techniques are proposed, each having certain relative merits. In all cases the resolution in capacitance is shown to be governed by a combination of the resolution in conductance, the sample properties, and the frequency of the measurement.
Measurement and Computation of Thermojunction Response Times in the Submillisecond Range
Authors: Balko Bohdan , Berger Robert L.
Published: February 2004

A simple method is presented for measuring the response of thermocouples in liquid media. Response times down to 50 μsec have been measured. Various coating techniques for obtaining fast responding electrically insulated junctions are discussed. The effect of thermocouple materials and insulation coatings on the response time has been experimentally determined and the results compared with a computer calculation simulating the physical system. The computer calculation involves two difference equations and solves a multilayered media problem without the introduction of heat transfer coefficients. The results agree to within experimental error.
Whole-Body NMR Spectrometer
Authors: Jackson Jasper A. , Langham Wright H.
Published: February 2004

A low-frequency NMR spectrometer has been built that will accommodate sample volumes of 0.2 and 1.25 liters. A shielded solenoid provides a uniform field of about 10 G. Signals are detected by a symmetrical rf bridge whose coils are bank wound of litz wire with Q∼300 to 400 at 40 kHz. In the smaller coil the homogeneity is sufficient to distinguish signals of protons in protein from those in fat and water. Spectra have been obtained from gelatin, whole eggs, egg whites, egg yolks, and dead mice. In addition, what is believed to be the first NMR signal ever obtained from a whole living animal has been taken on an anesthetized rat.
Technique for Accurate Measurement of the Electrical Conductivity of Shocked Fluids
Authors: Mitchell A. C. , Keeler R. N.
Published: February 2004

A method of accurately measuring the electrical conductivity of shock compressed fluids is described. It is shown that when optimum geometry is used and when the shock impedance of fluid and electrodes are properly taken into account, the effect of reflected shocks can be understood. Data for carbon tetrachloride over a pressure range of 65 to 160 kilobars and a conductivity range of 10−1 to 10−7 mho/cm are presented. The accuracy of the measurements is better than 10%.
Simple NMR Probe for Use in Superconducting Solenoids
Authors: Higgins R. J. , Chang Yung Kwang
Published: February 2004

A simple nuclear magnetic resonance probe, for field calibration use over the 10–50 kG magnetic field range in superconducting solenoids at liquid helium temperature, is described. The probe uses the 27Al resonance from aluminum powder, and is attached without electronic modification to a commercial NMR (marginal oscillator) gaussmeter.
Remote Control Viscometer
Authors: Cussler E. L. , Fuoss Raymond M.
Published: February 2004

A remote control viscometer, designed for use in a high pressure bomb up to 5000 atm, is described. Operation is as follows: a solenoid lifts a tapered piston, which then drops into a cylinder. On the down stroke, needles attached rigidly to the piston dip successively into two mercury wells, the first one starting an electric timer and the second stopping it. Three insulated leads into the bomb are required; the case acts as the common ground. Relative viscosities can be reliably measured within 2%. Results at 30° are given over the pressure range for n-propyl ether, cumene, n-butyl chloride, and 1,2-dichloroethane.
Microminiature Hall Probes for Use in Liquid Helium
Authors: Simpkins J. E.
Published: February 2004

A technique is described for the fabrication of microminiature Hall probes which perform reliably in liquid helium. These probes consist of vacuum deposited films of InAs and InSb, having a sensitive area of 25×25 μ and a thickness of 5000 to 10 000 Å. The InAs probe is capable of measuring magnetic field intensities of from 1 G to over 50 kG, and is relatively insensitive to changes in temperature and to thermal cycling. The InSb probe is extremely sensitive to magnetic fields and is useful in measuring magnetic field intensities in the fractional Gauss range.
Electron Gun Using a Field Emission Source
Authors: Crewe A. V. , Eggenberger D. N. , Wall J. , Welter L. M.
Published: February 2004

A new electron gun has been built which features mechanical and optical simplicity. Theoretically, it can produce a focused spot having a radius smaller than 50 Å and provide 1000 times more intensity than a hot filament system having a similar final spot size. The increase in intensity is made possible by using a field emission electron source operating at a pressure of 10−9 Torr, which is provided (without baking) using commercially available pumps. The small spot is produced by using two properly shaped electrodes which accelerate and focus the electrons from the tip. It would take a hot filament gun and at least two additional lenses to replace this field emission gun when a spot radius less than 100 Å is required. Even then the brightness of the conventional source would be too low to make use of the small spot size obtained. The optical properties for the new gun were predicted on a computer and experimentally confirmed in a new scanning electron microscope. The aperture aberration coefficient was measured to be no more than a factor of two greater than the theoretical value of 1.5 cm. A spot radius of 250 Å has been measured, and this value is to be compared with the theoretical value of 150 Å. Although it was convenient to measure the spot directly only at a relatively large image distance (11.3 cm), calculations imply that the gun can provide a spot radius less than 25 Å when very small image distances are used. The gun can be used in pulsed operation because all optical properties are constant for a given voltage ratio so that application of the electrode voltages by means of a voltage divider provides automatic focusing for arbitrary changes in the applied voltage. The methods used to make and operate reliable high field emission tips are reviewed, and a technique is described for changing the required tip voltage to obtain a given emission current.
Technique for Decreasing Photographic Recording Time in Field-Ion Microscopy
Authors: Brenner S. S.
Published: February 2004

The exposure time to record field-ion images on 35 mm film, can be significantly decreased by reducing the diameter of the ion image to 2.5 cm and using 1:1 photography. By this means, ion images were recorded 10 to 20 times faster than with the usual image size of 8 to 10 cm. Visual observations of details of the reduced ion images can be made conveniently with a conventional stereomicroscope. Some of the factors affecting the quality of the ion-micrographs are discussed.
Evaluation of Refraction Errors in Interferometric Heat Transfer Studies
Authors: Schmidt F. W. , Newell M. E.
Published: February 2004

An evaluation of light refraction errors in interferometric heat transfer studies is reported. The differential equation describing the path of a light ray passing through an arbitrary thermal boundary layer surrounding a heated surface has been solved using numerical techniques. Results for cubic and parabolic temperature profiles have been presented. The method of analysis reported is of particular value in the estimation of the refraction errors in an experimental unit if an approximation of the temperature distribution in the boundary can be made. It is noted that these errors may be minimized by careful design of the test section. In many cases it is also possible to use these techniques to correct actual interferometric data for refraction errors.
Thermal Expansion of Epoxies between 2 and 300°K
Authors: Hamilton W. O. , Greene D. B. , Davidson D. E.
Published: February 2004

A simple apparatus for measuring relative thermal expansions down to very low temperatures is described. The thermal expansions are given for a number of commercial epoxy resins. The effect of loading epoxies with fused quartz powder is described. Several epoxies are found to match the thermal expansions of the common metals.
Laser Temperature-Jump Apparatus for Relaxation Studies in Electrolytic Solutions
Authors: Hoffmann Heinz , Yeager Ernest , Stuehr John
Published: February 2004

Temperature-jump apparatus for relaxation studies in electrolytic solutions has been developed with laser heating and conductivity readout. The apparatus is suitable for quantitative studies of relaxation times in the range 10−1 to 3×10−6 sec. With a ruby laser, an appropriate solute must be added to aqueous solutions lacking a colored solute to adjust the optical density of the solution to an appropriate value. With a neodymium laser, the intrinsic absorption of water in aqueous solutions is adequate.
High Energy γ-Ray Detector with Good Resolution
Authors: Dally E. B. , Hofstadter R.
Published: February 2004

A 12.7×12.7 cm cylindrical lead fluoride (PbF2) crystal has been tested as a Čerenkov shower detector of high energy positrons. The behavior is expected to be similar for electrons and γ-rays of the same energies. The line width (full width at half-maximum) varied from 32% at 300 MeV to 16% at 900 MeV. A linear relationship between pulse height and energy was observed over the measured range.
Capacitance Methods for Measuring Properties of Adhesives in Bonded Joints
Authors: Rutherford John L. , Bossler Fred C. , Hughes Edward J.
Published: February 2004

Two capacitance-type methods are described, one of which can be used for measuring the stress-strain behavior and the other for the strain-sensitive electrical properties of the adhesive material used to bond two metallic adherends. In cases where the electrical properties of the adhesive are insensitive to strain, both techniques can be used to measure the stress-strain behavior. The first method uses an externally mounted, air gap, capacitance-type extensometer mounted on the adherends very close to the adhesive joint. In the second method, the adherends are the capacitor plates and the adhesive serves as the dielectric medium. Load-unload tests using butt joints have been made in tension and compression. The data are obtained as X-Y recordings where the X axis is the output of a capacitance bridge and the Y axis is the load applied to the joint. Capacitance sensitivities are on the order of 5×10−4 pF/div. (8 div./cm on the X axis). When calibrated for extension, the X axis sensitivity is about 1.3×10−6 mm/div. Thus, capacitance-load and extension-load behavior may be recorded. When the adherends are used as the capacitor plates, the observed extension is from the adhesive material alone; deformation in the adherends is not recorded. When a load is applied, the capacitance changes because the plate separation is altered and the electrical properties of the adhesive material may be affected by strain. For those materials whose electrical properties are strain-sensitive, the data are backed up by the air gap extensometer which establishes the plate separation due to loading, independent of any electrical property changes in the adhesive material. Thus, the strain sensitivity of the electrical properties may be established. Typical results on three different polymeric adhesives are described; these results illustrate the use of both techniques.
Differential Isothermal Microcalorimeter: Heats of Mixing of Aqueous NaCl and KCl Solutions
Authors: Picker Patrick , Jolicoeur Carmel , Desnoyers Jacques E.
Published: February 2004

A differential microcalorimeter operating under vacuum has been designed for the study of solutions. Constant and equal heating is supplied to twin cells which are in contact with a constant temperature cold source. A temperature variation produced in the working cell is detected by a thermistor bridge; the signal from this bridge serves to control the rate of heating in the working cell such that the appearing temperature difference is cancelled. The response time of the instrument is less than one 1 min and its sensitivity is 5 μcal; heat effects larger than 10 mcal can be measured to 1% or better. The heat of mixing of aqueous solutions of KCl and NaCl at 25°C have been measured between 0.1 and 1.2 molal.
Linear Electronic Chopper and Shaper for Sliding Pulse Generators
Authors: Millard J. K.
Published: February 2004

An electronic chopper and shaper was developed to perform the function of a mercury-wetted relay in linear pulse forming applications such as required for sliding pulse generators. The chopper and shaper was operated at repetition rates up to 5000 Hz with a 2.2 μsec decay time constant. With a 100 Ω load, output pulses of 10 V amplitude had a rise time of 12 nsec. Tests performed with a 4096 channel pulse height analyzer showed no difference in spectra generated by this chopper and by a mercury-wetted relay chopper. Static checks indicated the differential nonlinearity to be about ±0.1% for an output range from 20 mV to 10 V across a 100 Ω load.
Precision High Speed Current Regulators for Occasionally Switched Inductive Loads
Authors: Redfield Alfred G. , Fite Warner , Bleich Hermann E.
Published: February 2004

Power supplies used in field-cycling nuclear resonance experiments are described. These are used to switch an air coil from high field to low field as rapidly as possible, then back to high field after a short time. This sequence must be repeated every few seconds or minutes. An example of a simple regulator is described, and methods of output switching with relays are discussed. A circuit is described which delivers up to 10 kG (15 A) in a 2.6 cm i.d. superconducting coil with a switching speed of 5×105 G/sec and an accuracy probably as great as 1 G. Speed is achieved by automatic connection, during up or down switching, of energy storage capacitors across the magnet, operating at much higher voltage than the steady-state voltage level across the magnet and pass transistors.
Pulse-to-Analog Converter for Optimizing Signal-to-Noise from Photomultipliers at Low Light Intensities
Authors: Akins D. L. , Schwartz S. E. , Moore C. Bradley
Published: February 2004

A simple circuit is presented which is designed to discriminate and shape pulses from photomultiplier tubes and to provide an output suitable for analog recording. This circuit may readily be inserted between the photomultiplier and existing analog signal processing equipment. Signal-to-noise measurements are given for a cooled photomultiplier, with and without the pulse shaping circuitry. This circuitry affords a significant gain in the signal-to-noise ratio for a cooled phototube under conditions of low light flux when used in an analog system. We have found that the resulting signal-to-noise is governed by counting statistics alone.
Apparatus for Measurement of Transport Properties of Photocarriers in Insulating Crystals
Authors: Borders J. A. , Hodby J. W.
Published: February 2004

A pulsed detection system developed for the study of photoexcited carriers in insulating crystals is described. Positive and negative voltages are repetitively applied to the specimen placed between blocking electrodes. Transient photocurrents are then excited by repeated xenon flash illumination and detected by a transistorized charge-sensitive preamplifier. The pulses are amplified by a linear pulse-amplifier and averaged by a two-channel boxcar integrator. Photocurrents may be directly plotted as a function of some external parameter, such as temperature or magnetic field. The rms noise of the input stage is equivalent to a single charge pulse of 450 electrons but repeated pulses of 5 electrons each can be detected by averaging over a period of 90 sec. A differential technique used in cyclotron resonance experiments is described.
Apparatus for the Production and Ignition of Metal Droplets with a Pulsed Laser
Authors: Nelson L. S. , Richardson N. L. , Prentice J. L.
Published: February 2004

An apparatus is described which forms and ignites single metal droplets in a controlled atmosphere chamber with a single pulse of focused radiation from a Nd-doped glass laser. Before heating, tiny bits of metal-spheres, granules, or squares of foil-are supported in the laser focus either on crossed fibers of the same metal or in an electrostatic levitation device. Photographs of burning droplets at high magnification, complete trajectories, radiant emission histories recorded with a photomultiplier, and time-resolved emission spectra are presented as examples of the information that can be obtained with the apparatus.
Transistor Regulation System for Fine Current Control of an Arc Jet
Authors: Jenkins Richard C. , Hoff Marc
Published: February 2004

A current regulator was built to reduce fluctuations in arc-heated flows and to maintain set values of arc current for long periods of time. Regulation is obtained with 145 transistors in a three-stage assembly that is operated in series with the arc and is designed for use at current levels up to 1000 A. Results are presented that show its operating characteristics, its effect on arc current oscillations, and the corresponding reduction of fluctuations in test section flow properties.
Miniature High Temperature Graphite Furnace
Authors: Chang Ji Young
Published: February 2004

The construction of a miniature high temperature graphite resistance furnace is described. It has the unique feature of enabling thermal cycling in vacuum up to 2800°C in a short period (30 sec/cycle). The heating time required to reach 2800°C from room temperature in a 10−5 Torr vacuum is 10 sec, and the cooling rate from 2800 to 800°C is 200 C°/sec.
Reduction of Cosmic Background in an X-Ray Proportional Counter through Risetime Discrimination
Authors: Gorenstein Paul , Mickiewicz Stanley
Published: February 2004

The method of background reduction by risetime discrimination has been applied to a large area proportional counter for use in an x-ray astronomy observation from a sounding rocket. Analysis of data from a recent flight has shown the system to be about 90% effective in reducing the non-x-ray background observed in the space environment for the energy range 3–10 keV that persists when anticoincidence guard counters are used while at least 80% of the x-ray efficiency is retained. The system is simple, compact and does not require any critical components.
Theory and Design of an Absolute Viscometer for Low Temperature-High Pressure Applications
Authors: Kao James T. F. , Ruska Walter , Kobayashi Riki
Published: February 2004

A capillary tube absolute viscometer which is capable of measuring viscosity of a gas from above ambient to very low temperatures, with pressures up to 500 atm, has been designed and constructed. The viscometer has the unique feature of being applicable to low temperatures with the entire flow system maintained at the same temperature. The necessary equation for calculating viscosity measured on this viscometer has been derived. The proximity to and deviation from steady state operation for the viscometer have been clarified analytically. The analysis shows that the deviations from steady state are particularly important at low pressure.
Low Energy Electron Diffraction Apparatus Designed for Thin Film Use
Authors: Caldwell C. W. , Müller K.
Published: February 2004

For the study of thin epitaxial films by LEED it has been necessary to design a vacuum system more versatile than the system now in use. The vacuum and electron optical requirements are basically the same as for previous LEED systems. The additional requirements for thin epitaxial film studies are more precise control of evaporation sources, multiple sources, and thickness monitoring equipment. This paper describes an all-metal system built to meet these requirements. To allow room for a manipulation of evaporation sources, the vacuum system is of the metal bell jar type with directly attached ion-type pumps (100 liters/sec) plus a large area sublimation pump (1500 liters/sec). A mercury diffusion pump system is attached via a bakeable valve for prepumping and noble gas pumping. Three or more evaporation sources can be positioned to individually check their outgassing rate, check their evaporation rate and evaporate on the sample substrate. Rate of evaporation can be checked before evaporation on the substrate by a quartz crystal monitor or ion gauge type monitor. Also the total amount of material evaporated at the sample can be recorded directly or in reference to the change in conductivity of the deposited film. Sample holders can be of two types; one that can be heated to high temperature or cooled close to liquid N2 temperatures or a Dewar type coolable to liquid He temperatures. The two types of holder require a different evaporator arrangement. The high speed of the sublimation pump removes active gases liberated during operation of the evaporator. This eliminates the problem of large changes of background pressure during operation. The diffusion pump allows removal of noble gases after ion sputtering of the sample. Preliminary data obtained from the system indicate that the design is much more useful for thin epitaxial film studies than systems presently in use and it is probable that a similar versatility will be important for other applications.
Amplitude Stabilization of a Single Mode, 6328 Å, He–Ne Laser
Authors: Hansen J. W. , Rodgers K. F. , Thomas D. E.
Published: February 2004

Described in the following paper is a system for amplitude regulating the output of a single mode He–Ne laser in a band from dc to 200 cps. Over periods of ½ h the output was stabilized to about ±0.15% and to ±0.01% for periods of 40 sec. Since the regulator employs negative feedback, we also briefly discuss techniques for producing a stable system.
Some Properties of Gold-Iron Thermocouple Wire
Authors: Rosenbaum Ralph L.
Published: February 2004

Gold wire with nominal 0.02 at.% iron manufactured by Sigmund Cohn has been calibrated vs Hoskins' Chromel-P from 0.4 to 85°K. The high sensitivity of this dilute solution, its reproducibility upon cycling from room temperature, and stability upon aging were favorably confirmed. Thermopower variations on the order of 0.3% have been detected in spools of wire arbitrarily drawn from the 0.02 at.% bar. Thermoelectric emf measurements upon a recently cast nominal 0.07 at.% bar show potential variations smaller than 0.1%, thus allowing for accurate absolute temperature prediction from arbitrarily drawn wire. The Au–Fe thermocouple wire, particularly the annealed 0.02 at.% wire, is useful as an absolute thermometer down to 0.4°K owing to an anomalously high thermopower; however, individual lengths must be calibrated against a known standard if accuracies of better than ±0.05K° in temperature are desired below 1°K.
Laser-Triggered Spark Gap
Authors: Steinmetz Lloyd L.
Published: February 2004

A laser-triggered spark gap (LTSG) was developed to meet the need for producing a kilovolt electrical output pulse that is synchronous with the light output pulse of a Q-switched laser. The LTSG output pulse voltage is variable up to 12 kV, which value makes it usable for actuating Pockel cells. A theoretical explanation of the spark gap's triggering mechanism is developed.