bluuebunny/crossref_metadata_2025 huggingface dataset:
Cryostat for Neutron Diffraction Studies Between Liquid Helium Temperatures and Room Temperature
Authors: Sparks Joseph T. , Komoto Ted , Wade William R.
Published: February 2005

An efficient all metal cryostat is described for temperature dependent neutron diffraction studies in the range of liquid helium temperatures to room temperature. A modification of the Swenson type heat exchanger is employed in which the temperature is controlled by regulating the flow of cold gas or liquid through the exchanger by means of a precision needle valve. Using liquid helium in the system, sample temperatures in the range 2 to 100°K can be obtained. For fixed settings of the needle valve in the range for 4.2 to 40°K, the long term temperature drifts are less than 0.01°K/h. The short term periodic fluctuations are on the order of ±0.1°K or less. On one filling of liquid helium, the sample can be maintained for 2 days at any given temperature from just above the boiling point of helium up to about 100°K with an average loss rate of 25 cc of liquid per hour. The loss rate increases to about 45 cc/h when the sample is held at 4.2°K. Using liquid nitrogen in place of liquid helium in the temperature control system, sample temperatures between 77°K and room temperature may be obtained.
Phase Stabilized Vernier Chronotron
Authors: Kindlmann P. J. , Sunderland J.
Published: February 2005

A 500 channel system is described for measuring time intervals up to 1 μsec in 2 nsec increments. The vernier chronotron method of Lefevre and Russell is modified by the addition of a stable time base which phase-locks the circulation period of each loop and thus stabilizes the channel width. Solid state circuit elements are used throughout. The application of this time analyzer to the measurement of lifetimes of excited atomic states is discussed.
Plasma Potential Measurements by Electron Emissive Probes
Authors: Kemp Robert F. , Sellen J. M.
Published: February 2005

Several methods of using hot wire, electron emissive probes for potential measurements in quiescent plasmas are described. A plot of the probe emission characteristic gives a precise dc determination; the floating probe rapidly follows potential fluctuations of several volts magnitude; the cutoff slope detects small signals up to tens of megacycles per second. Calculations are discussed which describe the potential distributions around an emissive wire immersed in plasma, with and without the formation of a virtual cathode. Sheath dimensions are ∼10 wire diameters at 1010 ions/cm3; orders of magnitude larger at 106 ions/cm3. Emission levels appropriate to given plasma densities are shown. The range of application has a low density limit of ∼104 ions/cm3 because of minimum useful emitted current, and a high density limit of ∼1012 ions/cm3 because of electron collection from the plasma.
Sample Chamber for Magnetothermodynamic Measurements
Authors: Giauque W. F.
Published: February 2005

A single sample chamber designed for the determination of magnetic moment and susceptibility, heat capacity in magnetic fields, entropy change with field, temperature change during adiabatic demagnetization, and such derived quantities as magnetic work, free energy, internal energy, heat content, etc., as a function of field and temperature, is described. Field range of use is presently to 100 kG. Successive observations may be made with the solenoid field parallel to various axes without removing a spherical single crystal from the sample chamber.
Improvements in Linear Electric Shock Tube Drivers
Authors: Fowler Richard G.
Published: February 2005

A series of improvements in electric shock tube drivers is described, comprising a segmented series discharge driver for long duration flows, a segmented parallel discharge driver for large diameter shock tubes, a switchless shock tube for maximum circuit efficiency, and a metal walled driver for radiant energy conservation.
Apparatus for Continuous Differentiation of Data Curves
Authors: Chervenka C. H.
Published: February 2005

A new mechanical device is described which rapidly yields the derivative of a data curve in the form of a continuous plot. This table top differentiator, the operation of which is mostly manual, depends in principle upon the measurement of the slope of successive tangents to the curve. Slopes of numerical values between −1 and 5 are measured conveniently. The device has been applied to the differentiation of interference patterns from the analytical ultracentrifuge.
Technique for Streak Camera Writing Rate Calibration Using Pulsed Laser
Authors: Christensen A. B. , Isbell W. M.
Published: February 2005

A technique is described whereby the writing rate of a rotating mirror streak camera can be determined with the use of a pulsed laser and a knowledge of the speed of light. The result of using the technique to calibrate a 35 mm streak camera is discussed.
Technique for Simultaneously Measuring Ion Densities, Metastable Atom Densities, and Light Emission in Decaying Gaseous Plasmas
Authors: Sauter G. F. , Gerber R. A. , Oskam H. J.
Published: February 2005

An apparatus for simultaneously measuring the time dependence of (a) ion densities, (b) metastable atom densities, and (c) the intensities of spectral lines and bands during the decay period of a gaseous plasma is described. It is comprised of a quadrupole mass spectrometer for the ion density measurements and a light spectrometer for light emission and fractional light absorption studies. The reliability of the results obtained by mass spectrometer probing of a decaying plasma was checked by comparing the results obtained in helium with those obtained by other measuring methods. The data were found to be consistent and showed that this technique can be a significant tool for the study of collision processes occurring in decaying plasmas. Moreover, the simultaneous application of mass and light spectrometric methods gives information about the time dependences of the various plasma constituents at the same plasma region.
Effect of Intermodulation on Measurement of Small Hall Coefficients with Double ac Method
Authors: Suchannek Rudolf G.
Published: February 2005

The effect of intermodulation on the double ac method is described with emphasis on the mixing of the sample current frequency with the frequency of the magnetic field in the current circuit of the apparatus. The resulting voltages at the same frequency as the Hall voltage are coupled to the Hall voltage measuring circuit by the probe misalignment and the mutual inductance of the leads. Methods to eliminate the disturbing effects due to intermodulation are discussed.
Voltage Output Characteristics of Axial Gradient Heat Flux Transducers
Authors: Kinzie Phillip A. , Sosa Estanislao N.
Published: February 2005

An analysis is given for transducers employing thermoelectric temperature difference sensing as a measure of heat flowrate. A theoretical equation relating transducer output voltage to the applied heat flowrate is developed, based upon a simple model. This equation is shown to be a nearly linear function in the case of transducers employing copper-constantan-copper difference thermocouples. Experimental calibration data obtained using a conductive heat source are then compared with theory. The theoretical and experimental results are found to be in general agreement. It is concluded that transducers of this type demonstrate a voltage output function which is linear within the order of ±1%.
Multistage Gun for Production of Low Energy Ion Beams
Authors: Haskell H. B. , Heinz O. , Lorents D. C.
Published: February 2005

An ion gun using separate acceleration and deceleration stages to produce ion beams in the 1–100 eV energy region has been constructed and tested. The gun is based on an existing electron gun design but uses a thermal emitter Li2O·Al2O3·nSiO2 (n = 2 and n = 4) as a source of Li+ ions. Current densities of 10−8−10−6 A/cm2 at beam energies of 2–100 eV were obtained and both the spatial and the energy distributions of the ions were investigated. Minimum beam radii (typically about 1 mm) occurred a few centimeters from the last aperture. Beam profiles were measured as a function of axial distance and well collimated beams up to 16 cm in length were obtained. The energy spread in the beam was found to be 0.22 eV (total width at half maximum intensity), in good agreement with the expected thermal energy spread from the source which operates at about 1200°C. Mass analysis shows that beam purities are in excess of 99% 7Li+ for isotopically enriched emitter material. Theoretical calculations of space charge effects on image distance and image size are presented as well as design parameters and graphs for the operation of the gun under various conditions.
High Temperature-High Pressure Cell for Measuring Densities of Metals by Radiation Counting Technique
Authors: Dillon I. G. , Nelson P. A. , Swanson B. S.
Published: February 2005

Equipment and techniques have been developed for measurement of densities of metals at high temperatures (up to 2200°K). The equipment and techniques were demonstrated using alkali metals but are generally applicable not only to most metals but also to many other substances. Determination of vapor and liquid densities of alkali metals at high temperatures and pressures was accomplished by measuring the radiation emanating from the vapor and liquid phases of a radioactive alkali metal contained in a high pressure cell fabricated from a molybdenum-30 wt.% tungsten alloy. The procedure was used to obtain vapor and liquid phase densities of the alkali metals at temperatures up to 2200°K and pressures up to 500 atm, which approach critical conditions. The radiation counting method involves sealing the metal whose density is to be measured in a containment capsule, irradiating the capsule and metal to produce a gamma emitting isotope of the metal, charging the capsule into the high temperature cell, and counting the activity of the vapor phase and the liquid phase at temperatures ranging from room temperature up to the critical point. A calibration of density vs irradiation level is performed at low temperatures where accurate liquid density data are available.
Sieving for Particle Size Distribution in 10 Through 1 μ Region
Authors: Carroll H. B. , Akst I. B.
Published: February 2005

Sieves were used to determine particle size distributions smaller than 44 μ (usually considered the subsieve region) through 1 μ. In particular, sieves having openings of 10 through 1 μ were used to measure the distribution of high explosive particles which are approximately spherical. Particle size distributions agreed well with distributions obtained by microscopy and photosedimentometry. The sieves are electroformed ``micromesh'' screens in 7.6 cm diam nesting cylinders, like standard sieves in the large ranges. The proper choices of elutants, dispersion techniques and agents, and sample size have been important in obtaining reproducible results. Samples as large as 0.4 g are satisfactory. The time required to obtain a distribution analysis is somewhat dependent on sample size. With samples much larger than are usual with other ``subsieve'' measurement methods—e.g., 0.4 g—one technician completes two analyses with one set of sieves (<44 through <1 μ) in a normal day.
Design of Photomultiplier Socket Assembly with High Gain and Clean Output Signals for Tubes Viewing Organic Scintillator Light Pulses
Authors: Gibson William A.
Published: February 2005

Two of the major problems in designing a socket assembly for a 56AVP photomultiplier viewing light pulses from an organic scintillator have been investigated. They are (1) optimization of the dynode voltage distributions for gain and pulse shape over a wide range of tube gains, and (2) proper grounding of the dynode bypass capacitors and coupling of the coaxial signal leads to the anode and dynodes so that clean signals appear at the output. The effects of varying the dynode voltage distributions were studied and results of improper distributions are discussed. A dynode voltage distribution is given which gave near optimum gain and pulse shape for several different 56AVP's viewing the light pulses from an organic scintillator illuminated by 239Pu alpha particles over a wide range of supply voltages and with anode currents up to 1 A. An electrical and mechanical layout is presented which results in electrically clean pulses from the 14th dynode and anode as well as clean integrated pulses from the lower dynodes; in addition, high gain is realized with adjustment of only the last dynode-to-anode voltage. Photographs of the output signals are shown for a wide range of tube gains, and curves of the relative gain and risetime as a function of tube voltage are given.
Probe Cryostat to Fit He Supply Dewar
Authors: Schmitz J. A. , Ford D. R.
Published: February 2005

A design for an economical cryostat-probe is presented. Approximately 0.5 liter of liquid 4He is required to cool the probe and sample assembly. Sample temperatures are varied by using a heater and a thermal leak, with no appreciable loss of 4He noted during the heating-cooling cycles. Temperature regulation was held to ±0.005°K for extended periods of time. Provisions for magnetic field measurements have been included in the design of the probe.
Dispersion Relation and Frequency Characteristics of Alternating Periodic Structure for Linear Accelerators
Authors: Nishikawa T. , Giordano S. , Carter D.
Published: February 2005

For linear acceleration of high energy protons an alternating periodic structure operated in a ½π standing wave mode has the advantage of relative immunity from beam loading and detuning effects while sacrificing little in shunt impedance when compared to π mode operation in a uniform periodic structure. The dispersion curve of the alternating periodic structure is derived from an analysis of a chain of coupled cavities, in each of which the fields are expanded in normal modes. By introducing the effect of coupling between alternate cells in addition to adjacent cell coupling, the passband of any one cavity mode is then found to split into two unequal passbands separated by a stop band, the width of which depends on the structure's geometrical parameters. The relative distribution of energy between cells is also found as a function of frequency. Measured dispersion curves were used to check the theory and the dependence of theoretical parameters on structure geometry. It is shown that the stop band may be reduced or eliminated simply by introducing a fixed detuning of one of the two different alternating periodic cells. It is also shown that the advantages of reduced beam loading and detuning effects resulting from operation in the ½π mode is obtained even when the group velocity vanishes, as occurs in a split passband.
Surface Ionization Source of Cesium Ions
Authors: Kuskevics G. , Thompson B.
Published: February 2005

A surface ionization source using spherical powder porous tungsten generates up to 9 mA of cesium ions with only a few percent of neutral atoms.
Omegatron Mass Spectrometer for Partial Pressure Measurements in Upper Atmosphere
Authors: Niemann Hasso B. , Kennedy Brian C.
Published: February 2005

A simple Omegatron mass analyzer used for measuring density and temperature of nitrogen in the 100 to 350 km region of the upper atmosphere has been developed. The mechanical and electrical configurations have been designed for rocket flight application, and the operating parameters optimized for the upper atmosphere measurement. This Omegatron is calibrated and flown as part of a sounding rocket experiment known as the Thermosphere Probe, which also contains an electron temperature probe for determining electron temperature and density. Several successful flights have shown that the Omegatron is a reliable device for this application.
3He Cryostat for Operation to 0.2°K
Authors: Walton D.
Published: February 2005

A cryostat is described which is capable of somewhat lower operating temperatures than has previously been possible. This improvement has been achieved through the use of a pumping line to the 3He which is of larger than normal diameter, particularly at the low temperature end. Therefore, it is concluded that the major limitation in previous designs has been the pressure drop in the pumping line.
Small Neutron Beam Chopper
Authors: Whittemore W. L.
Published: February 2005

A simplified variable speed, rotating mechanical beam chopper has been developed for reactor neutron spectrum measurements, and for use in conjunction with a crystal spectrometer for inelastic neutron scattering measurements. Neutron pulses are produced with a time jitter which is small compared to the time between pulses, the rotor speed during runs of several hours being constant to at least 5%. Rotor designs for beam sizes of 1.59×4.45 cm have been successfully used for neutrons with energies up to 1.0 eV and with a transmission of about 80%.
Computer Designed 805 MHz Proton Linac Cavities
Authors: Hoyt Harry C. , Simmonds Dennis D. , Rich Walter F.
Published: February 2005

A numerical mesh calculation which computes the fields and frequency for a resonant cavity has been developed. Fields for any cavity which has cylindrical symmetry, and for which the magnetic field has only a θ component, can be computed. The program has been used on the IBM 7094 to study 805 MHz proton linac cavities. These design studies have shown that cavities having curved walls and triangular drift tubes give improved performance. Calculated values of ``shunt impedance'' per unit length ZT2 for such cavities range from 32.4 MΩ/m at β=v/c=0.45 to 53.0 MΩ/m at β=1. Experimental measurements have verified the calculations.
System for Suppressing Large, Nonstatistical Noise Bursts in Digital Averaging
Authors: Goodman L. S. , Salter F. O.
Published: February 2005

A device which eliminates the effect of noise bursts that exceed the average signal rate of digital data by more than a chosen, preset amount has been designed, constructed, and is herein described.
Calibration of Torsion Wires and Spurious Forces in Torsion Knudsen Effusion Recoil Measurements
Authors: Freeman Robert D. , Gwinup Paul D.
Published: February 2005

Within an experimental error of ∼0.3% the static and the dynamic torsion constants of selected small tungsten wires are equal. It is suggested that spurious forces which have been observed in torsion Knudsen effusion recoil measurements arise from thermomolecular flow rather than from torsionally anisotropic wires.
Probe for Measuring Ion Density in Slightly Ionized, High Speed Flow
Authors: De Boer P. C. T.
Published: February 2005

A probe made of a hollow glass cylinder is placed with its axis parallel to a slightly ionized, high speed flow. Biased electrodes on the inside surface collect the ions and the electrons entering the probe. The charged particle density is obtained by dividing the collection current by the product of the probe entrance area, the gas velocity, and the charge per particle. In order to establish that all charged particles entering the probe are collected, it is verified that no particles are attracted by a pair of auxiliary electrodes downstream of the main ones. Proper functioning also requires negligible charged particle production inside the probe, and furthermore that the velocity of the charged particles at the probe entrance be equal to the flow velocity. The probe was used to obtain ion density profiles behind shock waves of Mach numbers 6 to 9 in air at initial pressures of 50 to 400 μ Hg. Ion densities measured were in the range 107 to 1010 cm−3. Above this range, total collection was prevented by space charge effects. The equilibrium ion densities measured are in satisfactory agreement with theory. The values obtained for the ionization relaxation time are probably influenced by the presence of impurities.
Measurement of Currents Flowing through Electrode in Contact with Plasma
Authors: Haegi M.
Published: February 2005

Currents flowing through an electrode, in contact with a plasma, can be measured by inserting Rogowsky coils in the electrode itself. In order to avoid uncontrollable shunting of the current and damage of the coil owing to the plasma, a thin metallic foil is inserted between the coil and the plasma. The effects of such a screen on the measurements are calculated and compared with experimental results.
Growth of Cobalt Crystals
Authors: Hudson Hugh T.
Published: February 2005

A method of growing cobalt crystals by the Bridgeman technique is given. Crystals are grown in vacuum utilizing induction heating as the power source. Cobalt crystals in the hexagonal phase have been obtained 0.95 cm diameter by 6.26 cm long.
Wide Band Electrostatic Probes for Use in Tenuous Plasmas
Authors: Sprott J. C.
Published: February 2005

A derivation is given for the resistance of the sheath surrounding a floating probe and the corresponding limitation to the frequency response. The bandwidth is increased by using probes with built-in attenuators which measure fluctuations in floating potential, electric field, and ion saturation current at frequencies up to 40 MHz with plasma densities as low as 109 cm−3.
Dual Beam Stopped Flow Spectrophotometer Utilizing Modulated Xenon Arcs
Authors: DeSa R. J. , Gibson Q. H.
Published: February 2005

This paper describes a dual beam stopped flow apparatus for quantitatively observing rapid (up to 250 sec−1) chemical reactions in turbid suspensions. The unit employs two commercial 150 W xenon arc light sources modulated to produce square light pulses at 5000 cps; two wavelengths of light are selected by monochromators, and the light is delivered to the reaction cuvette of a conventional stopped flow apparatus via a fiber optic light guide ``Y.'' Current and light intensity feedback are utilized to control lamp intensity; simple transistor choppers demodulate the measuring photomultiplier output, and a second photomultiplier is utilized in a differencing scheme to reduce effects of residual lamp instability. The instrument has a limit of detectability of 1×10−3 optical density units; crosstalk of signal from one channel into the other channel is 6% of the change being measured. An example of instrument performance is presented; as now constructed, the instrument provides time resolution at least 5 times higher and reagent economy more than 20 times higher than other available dual wavelength spectrophotometers.
High Temperature Alumina Discharge Tube for Pulsed Metal Vapor Lasers
Authors: Piltch M. , Gould G.
Published: February 2005

An alumina high temperature gas discharge tube with cold windows has been constructed for the investigation of metallic vapor lasers. It offers vacuum tight containment to 1400°C, and flexibility with respect to active material, discharge diameter, type of excitation, and output windows. Pulsed laser oscillations in lead, manganese, and copper have been observed in this apparatus.
Gas Flow Proportional Counter for Electron Probe Light Element Analysis
Authors: Vogel Raymond S. , Fergason Lewis A.
Published: February 2005

A gas flow proportional counter designed for use as the detector in a microprobe nondispersive system is described. The counter design incorporates (1) relatively low operating voltage with high multiplication factor, (2) an anode wire support to minimize ``end effects'' on the pulse height distribution curve, and (3) an over-all design to permit convenient disassembly and replacement of the anode wire or other components. Results of performance studies indicate higher resolving power than similar commercial counters and negligible shift in multiplication factor over a wide range of counting rates.
Time-of-Flight Spectrometer for Laser Surface Interaction Studies
Authors: G. E. Bernal , Levine L. P. , Ready J. F.
Published: February 2005

A specially designed time-of-flight spectrometer has been constructed for studying the ions emitted from an opaque surface in vacuum under bombardment by a Q switched laser beam. Since some of the ions to be studied are emitted with considerable kinetic energy, the spectrometer allows one to make independent measurements of the m/e of the ions and of their initial kinetic energies. No other spectrometer design permits simultaneous measurements to be made of these two parameters during the interval of a single laser pulse. The design considerations involved in the construction of this spectrometer are described in some detail.
Recording Arrangement for Determining Temperature Dependence of Paramagnetic Susceptibility
Authors: Ellenkamp L. A.
Published: February 2005

The article describes the setup and functioning of an arrangement that can be used for carrying out susceptibility measurements over a temperature range from −150 to +1200°C. The measured result is continuously recorded.
Transverse Microwave Cavity Technique for Sensitive Measurement of Transient Electron Density Distributions
Authors: Lubin M. J.
Published: February 2005

A high resolution transverse microwave probing technique is described utilizing radiating slots cut in an oversize waveguide containing the plasma. General expressions for the transmission coefficient of the doubly infinite cavity are derived and applied to the measurement of precursor electron density distributions in an electromagnetic shock tube. The results compared favorably with the results of other independent measurements.
Rapid Photometric Method for Increasing Precision of Layer Thickness Measurement by Angle Lap Technique
Authors: Dudley R. H. , Briggs T. H.
Published: February 2005

A densitometer has been used for location of two beam reflected interference fringes in the measurement of layer thicknesses. Routine measurements of layers of approximately 3000 Å thick were repeatable within less than 350 Å. The precision depends primarily upon the quality of the sample preparation. Two instruments of widely different price and resolution were used, yielding essentially equivalent results. Photographic prints and transparencies were used as densitometer samples with equal success.
System for Observing Small Nonlinearities in Tunnel Junctions
Authors: Adler J. G. , Jackson J. E.
Published: February 2005

A system using a combination of harmonic detection and bridge techniques for the measurement of dV/dI and d2V/dI2 of superconducting tunnel junctions having resistances ranging from a few ohms to several thousand ohms is described. These quantities are of fundamental interest in the study of the density of electron states and phonon spectra of superconductors. This system is capable of determining σ=(dV/dI)n/(dV/dI)s, the relative dynamic conductance, where dV/dI is the dynamic resistance of the junction in the normal (n) and superconducting (s) state to within a few parts in 105. This high resolution is achieved using very small modulation levels of 60 μV rms (kT at 1°K=86 μV rms) or less. Finally, circuitry for obtaining dI/dV in the region near the energy gap using extremely low modulation levels (5 to 10 μV rms) and capable of resolving the negative resistance region is also presented. Typical data obtained with this system are shown.
Gap Loss Function and Determination of Certain Critical Parameters in Magnetic Data Recording Instruments and Storage Systems
Authors: Wang H. S. C.
Published: February 2005

After a brief review of Westmijze's semi-infinite model for the reading of recorded signals in magnetic media by gapped ring heads, a program for the computation of the gap loss function S is described. By introducing the higher order sine and cosine integrals, this function can be evaluated to any degree of accuracy over its useful range. A four decimal place table is compiled and included in this report. Two experiments significant to the validity of the theory and the practical evaluation of the data system performance were carried out with the help of the table compiled. By autocorrelating the system output, the null points in the frequency response curve of tenths of micron (micro-inch) gaps were located with confidence. The first null point determines the effective gap length accurately, from which the signal amplitude reduction due to gap interference at arbitrary wavelengths can be calculated. Further measurement of output signals at three suitably chosen frequencies enables one to determine the effective thickness of magnetization and head medium separation. The good agreement of the theoretical response curve based on these parameters with the directly measured data indicates the general validity of Westmijze's model. From a practical point of view, the knowledge of these parameters makes it possible to separate the signal amplitude losses during reading operation and suggest proper approaches to the improvement of system resolution.
Self-Illuminated Schlieren System
Authors: Watermeier Leland A.
Published: February 2005

A self-illuminated schlieren system was developed for use in studying phenomena which may have light intensity so great as to mask external light sourcs. Examples of such phenomena might be plasma jets or solid rocket propellent combustion where metal additives are present. The optical layout is described in detail and photographs are presented to illustrate its use.
Bright, Submicrosecond, High Pressure Spark Discharges of Light
Authors: McMahon D. H. , Franklin A. R. , Carleton H. R.
Published: February 2005

The characteristics of spark discharges in confined volumes of the gases nitrogen, carbon dioxide, argon, and helium are measured in the pressure range from 1 to 40 atm. It is found that both the brightness and efficiency of the discharge increase rapidly with pressure. The results of this investigation show that high pressure spark discharges can be used to produce extremely bright submicrosecond pulses of light having peak luminous powers in excess of 105 W radiating into 4π sr over the wavelength range from 3200 to 7000 Å. Because the luminous area is localized to 0.01 cm2, a brightness of 107 W/cm2 is readily obtained.
Lithium Compensated Silicon Focal Plane Detectors for Electron Scattering Spectrometers
Authors: Dodge W. R. , Coleman J. A. , Domen S. R. , Whittaker J. K.
Published: February 2005

In order to utilize the inherent resolving power of a double focusing, 169.8°, 76.2 cm radius of curvature magnetic spectrometer being constructed at the National Bureau of Standards for elastic and inelastic electron nuclear scattering studies, focal plane counters were needed whose dimension along the direction of momentum dispersion was 1 mm. This paper describes the fabrication techniques and performance of lithium compensated silicon 1×1×60 mm radiation detectors which seem well suited for use as focal plane detectors for the above spectrometer. Differential and integral pulse height distributions for 10–40 MeV electrons incident on the counters are presented as a function of the temperature and bias voltage. Effects due to the finite width of the counters are discussed. A tunnel diode discriminator which provides the desired binary information to the NBS data processing system is described.
Field Emission Diode and Triode
Authors: Koyama Masaki , Kawai Hiroshi
Published: February 2005

The characteristics of field emission diodes and triodes with narrowly spaced electrodes were investigated. They could be used under comparatively low voltage. When the voltage between the anode and cathode was several hundred volts, the current was 10−12 to 10−4 A. The stability of the current, though it depends on the vacuum in the tube and on the pretreatment of the electrodes, was fairly good in this range (about 1%). The collector current of one of the triodes with two cathodes a small distance apart was varied from 10−11 to 10−6 A when the potential difference between the cathodes was changed by 400 V at a collector potential of 450 V.
High Stability ``Boxcar'' Integrator for Fast NMR Transients in Solids
Authors: Ware D. , Mansfield P.
Published: February 2005

An improved double channel electronic sampling integrator with digital output is described which is particularly suitable for enhancing signal-to-noise in pulsed NMR studies in solids where narrow sampling gate widths and long data memory are essential. The sampling gate widths are 1 μsec or less. The difference signal between the channel inputs is converted to digital form and stored in a standard counter which may be modified to add successive counts, thereby computing the mean numerically. Since there is no analog integration the system has a pulse response time of 1 μsec. The system is free of ion or grid current drift problems common to previous designs. Thermal drift is small. Details of the circuits and graphs of integrating performance are presented.
Device for Orienting Transparent Crystals by Use of Optic (c) Axis
Authors: Thomas R. A.
Published: February 2005

An apparatus for determining the c crystallographic axis of transparent uniaxial crystals is described. This system utilizes the crossed polarizer technique for locating the c axis. With this small portable device, irregularly shaped crystals, both large and small, may be oriented and polished to within 10′ in a relatively short time. This method is particularly useful for determining the c axis of crystals for fluorescence and absorption studies and for orienting long cylindrical optical maser crystals.
Direct Measurement of Convective Heat Loss from Human Subject
Authors: Carroll D. P. , Visser J.
Published: February 2005

A new method for the direct measurement of the convective heat loss from a human body working in a natural posture under different environmental conditions in a climatic chamber is described. The method is based on the integration of the increase in heat in the wake behind the body by the use of temperature integrating grids. A unique method of calibration takes account of the variation of velocity across the wake. An accuracy of better than 5% is expected with the method for normal test conditions.
Dual Path Ultrasonic Measurement of Fluid Flow
Authors: Brown A. E.
Published: February 2005

A dual path ultrasonic flowmeter has been developed in which the measurement of fluid flow and the speed of sound can be made with the same meter without major interdependence. By placing two sound-speed meters in opposition, sum, and difference frequencies can be extracted. The sum frequency is proportional to the speed of sound and the difference frequency to the velocity of the flowing medium. Small errors which arise from differential path lengths and time delays between the two measuring paths can be minimized by an iterative process of adjustment. Based on this technique, an instrument to measure flow in pipelines was developed and tested. The resulting flowmeter is considered to have an accuracy of 0.25%. By correction for changes in the speed of sound of the measured fluid, the accuracy can be increased to approximately 0.1%.
Continuous Averaging Technique for Avoiding Drift Effects in X-Ray Scattering Measurements
Authors: Peters C. R. , Milberg M. E.
Published: February 2005

A continuous averaging technique for avoiding the effects of long period drift in x-ray scattering measurements has been developed. Only minor changes in conventional diffractometer equipment are required. A high speed drive motor is substituted for the conventional one in the diffractometer, and the scattered intensities are stored on paper tape. Thus, the sum of many rapid scans is substituted for one slow scan and the effective drift time is reduced to a negligible value. The actual summation of scattering patterns in proper register is done with an electronic computer. The scattering patterns obtained in this manner are expected to provide better structural information than was previously available concerning amorphous substances. Comparison of conventional and continuous averaging scattering patterns with and without an artificially imposed drift demonstrates that the method is effective.
Product Type Phase Sensitive Detector of Long Integration Time
Authors: Holland Lawrence Rozier
Published: February 2005

A new synchronous detector has been built. Based on a resistive network and instrument thermocouples, it has a flat frequency response from 0 to radio frequencies. Bandwidth is reduced by thermal capacity in the thermocouples. Analysis provides design criteria of general utility and these criteria are applied to a prototype.
Extraction of Positive Ions from Electrodeless Discharge
Authors: Williams J. F.
Published: February 2005

The positive ion current extracted from an electrodeless discharge is studied as a function of the discharge parameters of oscillator input power and frequency, gas pressure, magnetic field, extraction voltage, and extraction electrode geometry. A greatly enhanced ion current is obtained by operating the discharge at a pressure of several microns of mercury and applying a static magnetic field either parallel or perpendicular to the magnetic component of the high frequency electromagnetic field. Mean beam energies up to 200 eV above the extraction voltage and beam energy spreads of 50 eV are observed and studied as functions of the discharge parameters.
Isothermal Plasma Oven
Authors: Agnew Lewis , Summers C.
Published: February 2005

A tantalum oven that produces quiescent isothermal cesium plasmas at precisely known temperatures and pressures is described. The apparatus consists of a closed, cesium vapor filled tube heated by radiation within a resistance heated vacuum furnace. Plasma temperatures up to 2300°K and cesium vapor pressures up to 10 Torr are obtainable. Temperatures are measured by calibrated unsheathed W/W-26%Re thermocouples. Cesium vapor pressures are known through careful control of the cesium condensation conditions. Designed especially for spectroscopic studies, the oven features two sapphire windows mounted on a line-of-sight axis through the plasma. Details of construction and operation are described. Performance data showing temperature profiles to 1% over a 10 cm length are given.
Distinguishing Between Positive and Negative Difference Frequencies
Authors: Ekstrom Philip A.
Published: February 2005

A modified heterodyne technique is suggested which produces one of two readily distinguishable outputs depending upon which input frequency is higher. Application is made to a direct reading angular position indicator based upon a laser rotation sensor.
Wide Range Thermostat for Mössbauer Spectroscopy
Authors: Sharon B. , Treves D.
Published: February 2005

A vacuum thermostat for Mössbauer effect studies permitting temperature control from 85 to 870°K is described. Any temperature in this range can be maintained for long periods, utilizing an appropriate electronic temperature stabilizer. Temperature inhomogeneity over the sample is estimated to be less than 1°K. This thermostat can transmit radiation with a conical angle of 12°. Operation is simple and samples can be quickly interchanged.
Electrostatic Aerosol Sampler for Light and Electron Microscopy
Authors: Liu Benjamin Y. H. , Whitby Kenneth T. , Yu Henry H. S.
Published: February 2005

A two stage electrostatic aerosol sampler capable of accurate sampling of micron and submicron size aerosols onto any flat collecting surface of an area up to 5×10 cm2 is described. Size classification of the deposited aerosol is prevented by the use of a novel pulsed precipitating electric field. Sampling efficiency and the uniformity of the deposited aerosol has been determined using monodispersed flourescent aerosols over the size range from 0.028 to 3.2 μ. The sampler has been found to be very satisfactory for obtaining aerosol samples for electron or light microscopy.
Xenon Plasma from Focused Coaxial Gun
Authors: Dunne Brian , Benham Benson P.
Published: February 2005

A technique has been developed for focusing a plasma beam from a coaxial accelerator which increases the plasma energy per unit area by a factor of fifteen or more without reducing the front velocity. The pressure, impulse, and power flux characteristics of a xenon plasma were measured outside the focusing device of the accelerator to optimize the operational parameters. The plasma pulse has a 107 cm/sec front velocity, and sufficient cross sectional area, density, duration, and uniformity to be useful in plasma-solid interaction studies at high power fluxes (∼45 to 100 MW/cm2), where radiation is the dominant mode of energy transfer.
Measurement of Microgram Surface Densities by Observation of Proton Produced X Rays
Authors: Christensen L. J. , Khan J. M. , Brunner W. F.
Published: February 2005

X-ray production by proton bombardment was used to determine the surface density of thin films of Al, Cu, and Yb. This was accomplished by comparison at a number of thicknesses with known films. In addition, the x-ray yield for Al was compared with values predicted by the use of x-ray production cross section, stopping power, and bulk density. The experimental and calculated values agreed within 15%. The data are presented in linear form from 0 to 1900 Å and semilogarithmic form from 0 to 7000 Å, which is nearly a thick film for this technique. The useful upper limit lies in the range of 1000 Å for Yb and 4000 Å for Al. The lower limit is not clearly established, although the measurements for the Al surface densities were limited to surface densities equivalent to 1.2 Å as established by substrate contamination.
High Sensitivity Zero Crossing Detector for Magnetic Resonance Lines
Authors: Hickmott J. T. , Kushida T. , Murphy J. C.
Published: February 2005

A system utilizing a time averaging computer (CAT) to determine the zero crossing of the derivative of the magnetic resonance lines with an improved accuracy is described. The programming sequentially selects only the essential sections of the resonance (derivative) curve to determine the zero crossing. These are an upper off-resonance, a near center, and a lower off-resonance part, and the CAT accumulates these signals. Thus the resulting resolution is not limited by the fixed number of channels in the analyzer, and more data can be taken in a given experimental time. To demonstrate the system, the zero crossing of the 27Al NMR line in Al metal was measured. An accuracy of the order of 1/1000 of the line width was attained, which is about 30 times better than conventional techniques.
Experimental Technique for Impulse Loading of Structures
Authors: Sennett R. E. , Isbell W. M.
Published: February 2005

An experimental technique for impulsively loading structures by utilizing a compressed-air gun is described. Structural models are accelerated to a prescribed velocity and stopped by impacting a long rod. Their response to the induced impulsive load is measured by high speed photographic techniques. Comparison of the theoretical and experimental response of an aluminum ring is presented and discussed.
Hydrostatic and Uniaxial Pressure Generation using Teflon Cell Container in Conventional Piston-Cylinder Device
Authors: Jayaraman A. , Hutson A. R. , McFee J. H. , Coriell A. S. , Maines R. G.
Published: February 2005

A technique has been evolved to generate hydrostatic and uniaxial stress regimes, using a Teflon cell as a container in a conventional piston-cylinder device. Details of the technique and calibration procedure are described. The possibility of using high resistivity as-grown n-GaAs for pressure measurement is indicated. Piezoresistive effects in oriented n-Si plates were used to determine the nature of stress distribution in the pressure medium. The usefulness of the technique to semiconductor studies is pointed out.
An Automatic Technique for Accurate Measurements of Seebeck Coefficient
Authors: Berglund C. N. , Beairsto R. C.
Published: February 2005

A simple and rapid automatic method for measuring the Seebeck coefficient of semiconductors is described. Provided that errors due to sample mounting and contacting are negligible, 1% accuracy can be achieved.
Maximum Ratings for Xenon Filled Linear Flashlamps
Authors: Perlman David E.
Published: February 2005

An approximate mathematical analysis of wall loading and energy dissipation is presented in lieu of comprehensive (and expensive) destructive testing, with the aim of extending previously published maximum peak current ratings for a given lamp type to flashtubes having various length/diam ratios and operating in multisection LC discharge lines (pulse forming networks). A second peak current rating, independent of pulse duration, is tentatively established in an attempt to predict failures from excessive current buildup rates.
Liquid Surface Electrostatic Precipitator
Authors: Strindehag Ove M.
Published: February 2005

A liquid surface electrostatic precipitator for fission product monitoring is described. The precipitation electrode is made of a double wire arrangement which guides a liquid flow. Collected activities are detected by means of a Čerenkov detector. The precipitator has been operated with water as the precipitation medium at a flow of about 0.5 cm3/sec. Experiments indicate a precipitation efficiency of 70% and a detector efficiency for 88Rb of up to 80%.
Microbeam Collimator
Authors: Samsky D. N. , Glass W. A. , Herndon H. V.
Published: February 2005

A collimator is described which restricts a beam of charged particles to a few microns in radial extent. The collimator is a double aperture device and provides a pressure differential of one atmosphere with no foil window.
Eddy Current Method for Low Temperature Resistivity Measurements
Authors: Daybell Melvin D.
Published: February 2005

A modified mutual inductance bridge incorporating a commercial phase-lock amplifier has been used to measure low temperature bulk resistivities in the range from 1 to 10 000 nΩ cm. No electrical contact is required with the spherical metal samples, so that possible heat leakage along electrical leads is eliminated, and measurements can be made below 40 mdeg Kelvin using a dilution refrigerator. The bridge circuit, capable of determining resistivity changes with a precision of better than 0.3%, is described.
Specific Heat Determinations by Pulse Calorimetry Utilizing a Digital Voltmeter for Data Acquisition
Authors: Kollie Thomas G.
Published: February 2005

A pulse calorimeter for measuring the specific heat of electrical conductors from 25 to 900°C is described. The technique employed was unique in that a digital voltmeter, which was capable of recording 400 readings per second to a readability of 0.1% of full scale, was utilized to measure the transient temperature and power signals requisite to the method. Using this technique, a calculated determinate accuracy of 99% was achieved. Measurements of the specific heat of high-purity iron from 25 to 900°C confirmed this calculated accuracy and were repeatable to within ±0.5%. The calorimeter was capable of measuring the specific heat rapidly at temperature intervals as small as 0.1 C°. Modifications are suggested to decrease the measurement errors to 0.5% and to increase the temperature range from −190 to 1400°C.
Automatic Ion-Beam Path Stabilizer
Authors: Evans Albert E. , Johnson Kent
Published: February 2005

A system has been built to correct the output of an ion accelerator for beam-path variations. Fringing current detected on collimating slits is used to adjust voltage levels on two sets of electrostatic-deflection plates which guide the beam. Design details and method of operation are described.
Single Mirror Normal Incidence Reflectometer
Authors: Esposito R. J. , Rothwarf F. , Kozul S.
Published: February 2005

An inexpensive single mirror reflectometer for specular reflectivity studies at nearly normal incidence is described. This design minimizes errors in the reflectivity which may occur as a result of spatial variations in both the detector sensitivity and the mirror reflectivity. The reflectometer has been successfully used for reflectivity measurements from 2 to 22 eV in a detector-sample chamber which is coupled to a McPherson vacuum ultraviolet monochromator.
Electroluminescent Panel as a Modulatable Light Source
Authors: Dickson L. D.
Published: February 2005

The electroluminescent panel can be used as a linear modulatable light source at audio frequencies. (Brightness vs voltage linearity is extremely good for modulation as high as 60%.) Linear operation is accomplished by operating the panels at three times the normal voltage with a carrier frequency of 10 kHz. The rapid aging and resultant light loss which normally accompanies operation under these conditions is eliminated through the use of an efficient heat sink.