bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Effect on Spectrometer Slit Width and Photomultiplier Sensitivity
Authors: Ozolins A. , Lineberger W. C. , Niles F. E.
Published: February 2004

Variations in intensity measurements at 5100 Å resulting from temperature changes have been recorded using a 0.5 m Ebert scanning spectrometer equipped with a dual unilateral curved jaw slit assembly. Photons were detected by either a S-13 or S-5 photomultiplier. The variations were found to be consistent with an effective change of −0.10±0.02 μ/°C in the width of the spectrometer slits and with sensitivity changes of −0.8 and −0.45%/°C for the S-13 and S-5 tubes, respectively.
Standing Wave High Energy Linear Accelerator Structures
Authors: Knapp E. A. , Knapp B. C. , Potter J. M.
Published: February 2004

The design and operation of resonant linear accelerator tanks suitable for use in high energy proton and electron linacs is described. It is shown that construction of these tanks to operate in the π/2 mode yields systems with extraordinary field stability. Theoretical expressions and corresponding experimental observations are obtained for the behavior of cavity chains operating in the π/2 mode. The synthesis of the side coupled cavity chain, a biperiodic chain which combines high acceleration efficiency with π/2 mode field stability, is described. Extensions of π/2 mode operation to nonperiodic chains is also demonstrated.
A Single-Ended ``Q Machine'' with Pulsed Emitter
Authors: Korn P. , Marshall T. C. , Schlesinger S. P.
Published: February 2004

A simplified version of a single-ended ``Q machine'' operating in the atomic beam mode is described. A highly ionized, low temperature, cesium plasma is generated from the contact ionization of a monatomic cesium beam on a conical, closely wound, hot tungsten, spiral filament. The filament is heated by repetitively pulsing the current passing through it to allow periods in time where no voltage appears across the hot tungsten surface. This technique eliminates the necessity of heating a solid tungsten plate by electron bombardment. Electron densities from 1×1010 to 4×1011/cm3 have been achieved at confining magnetic fields ranging from 0–3200 G. During the period in which the filament current is pulsed off, the filament, electron, and microwave radiation temperatures are all approximately equal.
Laser-Induced ``Spark'' Light Source for Drift Mobility Measurements in Wide Band Gap Solids
Authors: Gill W. D. , MacDonald R. E. , Greene D. B.
Published: February 2004

We describe the laser-induced breakdown in xenon gas, or at an air/glass interface, as a fast risetime, high intensity light source for drift mobility measurements in insulating wide band gap solids. The measurable carrier transit time is limited by the laser pulse risetime to 20 nsec. The peak emissive power measured as a function of wavelength was found to have a maximum corresponding to a temperature of 104°K. The integrated peak power of the breakdown at an air/glass interface was 2.5×103 W/sr. The source has been used to measure carrier mobilities under transient space-charge-limited current conditions in materials having band gaps ranging from 2.5 to 4.0 eV.
Apparatus for the Determination of Magnetothermodynamic Properties to High Fields at Low Temperatures Utilizing a Superconducting Magnet
Authors: Butera R. A. , Kissell F. N. , Stein R. L.
Published: February 2004

An apparatus for the determination of magnetothermodynamic properties to high precision and low temperatures utilizing the field produced by a superconducting solenoid is described. The use of effluent heat exchangers and high efficiency wiring thermal anchors to minimize the consumption of liquid helium coolant during operation is discussed. Measurements of the magnetization and differential susceptibility as a function of field or temperature, as well as the heat capacity at constant field, may be determined without removal of the sample from the apparatus. Measurements on single crystals in various axial directions as well as on polycrystalline samples may be obtained using this apparatus. A discussion of the precision and accuracy of the measurements with this apparatus is presented.
Short Duration Flash Photolysis Lamp
Authors: Hochanadel C. J. , Ghormley J. A. , Boyle J. W. , Riley J. R.
Published: February 2004

A flash lamp is described which produces a high energy, short duration flash with relatively little afterglow. The flash is constrained to an annulus between a tube and concentric rod. The resistance of the lamp damps electrical oscillations, and the geometry provides quenching surface for reducing afterglow. The flash duration, flash tailing, and light output are given as a function of xenon pressure, flash energy, and flash voltage. Typically, a 288 J flash has a width of 2.7 μsec at 50% of peak height and 7 μsec at 1% of peak height.
Detector for the Metastable Ions Observed in the Mass Spectra of Organic Compounds
Authors: Daly N. R. , McCormick A. , Powell R. E.
Published: February 2004

A sensitive ion detector is described that can record the normal and metastable components of the mass spectrum of an organic compound. Alternately it can suppress to a very high degree the normal spectrum and amplify the metastable spectrum. It can detect metastable transitions taking place on either side of the magnet on a sector type mass spectrometer and it can be used to examine the different fragmentation pathways in the decomposition of an organic ion. The use of the device as an energy selector is briefly discussed.
Microwave Discharge Source for Atomic and Molecular Beam Production
Authors: Brink Gilbert O. , Fluegge Robert A. , Hull Robert J.
Published: February 2004

An atomic and molecular beam source is described which overcomes disadvantages present in earlier types of microwave discharge sources. The source uses a resonant coaxial line which requires no tuning adjustments inside the vacuum system. No water cooling is required. The source operates efficiently over a wide discharge pressure range and for many different discharge gases.
Measurement of the ``Strength'' of Explosives by the Ballistic Mortar
Authors: Johansson C. H. , Sjölin T.
Published: February 2004

In the past, the ballistic mortar has been used extensively for comparative measurements of the explosion energy of different explosives. This paper describes a number of modifications of the mortar aimed at decreasing energy losses by gas leakage, heat conduction, and plastic deformation of the firing chamber. By these measures, the mortar energy has been increased by about 30% for the same quantity of explosive, and the new values agree with theoretical predictions based on calculated values of explosion energy and gas volume.
Autographically Recording Sensitive Gas Flowmeter
Authors: Wolfenden A.
Published: February 2004

A continuously recording gas metering system has been developed with a working range of 0.01 to 3 cm3 sec−1 for nitrogen. The instrument is of the conventional U tube hydrostatic type and is made autographically recording by use of a capacitance transducer. It has been used to meter the evaporated coolant in a deformation calorimeter.
Microsensor for Measuring Humidity
Authors: Lai J. R. , Hidy G. M.
Published: February 2004

A microsensor of cylindrical geometry, 0.015 cm diam or less, has been developed for measuring changes in relative humidity in a gas stream. The sensor works on the principle of impedance variations in a thin dielectric film with changes of humidity of the surrounding gas. The cylindrical shell of dielectric material on which the sensor depends is aluminum oxide. The sensor was found to be sensitive, in terms of either reistance or capacitance, to changes in relative humidity in the gas for relative humidities greater than 30%. The very small size of the humidity probe, combined with its relatively fast response time, makes it useful for measuring gradients in humidity near moist surfaces, or for measuring concentrations of water vapor in turbulent media like the earth's atmosphere.
Technique for Studying Interactions between a Body Moving at Supersonic Speeds and Blast Waves Approaching Obliquely
Authors: Damkevala R. J. , Zumwalt G. W.
Published: February 2004

A technique has been developed for studying the oblique shock-on-shock interactions between a rifle-launched 19.5° cone-cylinder model and a cylindrical shock wave from a shock tube. A sufficient number of photographs were obtained so that whole sequences of events at selected shock strengths and model Mach numbers could be studied. It was found upon analysis of the photographs that considerable pressure differentials must occur on the model during interaction with the oblique blast. The use of Freon-114 as the driven gas in the blast-producing shock tube gave rise to two favorable results: increased clarity of the Schlieren photographs and reduced speed of sound in the receiver.
Photoconductive Cell Temperature Controller for Heating with Thyratron Controlled rf Generators
Authors: Hamilton D. R.
Published: February 2004

A small, inexpensive, relative temperature controller is described for use with rf generators equipped with thyratrons. Visible radiation from an induction-heated work piece is sensed by a pair of CdS photocells in a bridge circuit capable of delivering signals of the order of ⅓ V/C° between 850 and 1400°C. An error signal is derived and used to drive a dc amplifier which is coupled to ac phase shifting bridges utilizing neon lamps and another separate set of photocells to control the thyratrons in the rf generator. The demonstrated stability is ±1 C° at 1400°C, and there is considerable evidence that the long term stability is much better than this.
Uniform Charged Solid Particle Production
Authors: Erin T. , Hendricks C. D.
Published: February 2004

A means of producing small uniform spherical solid charged particles is described. A perturbation is applied to a liquid jet which then breaks up into uniform droplets as a result of the Rayleigh instability. The droplets are charged by an electric field as they form. The charged droplets are then frozen by allowing them to fall into an environment whose temperature is below the freezing point of the material. The material used is sodium nitrite and the uniform particles can be produced between 90 and 150 μ in radius while falling a distance of less than 1.5 m.
Versatile Spectrophotofluorometer-Polarization Fluorometer
Authors: Witholt Bernard , Brand Ludwig
Published: February 2004

A highly versatile spectrophotofluorometer with unique optical as well as electronic features is described. In addition to corrected excitation, emission, and polarization spectra, absorption and transmission spectra can also be produced. Spectra may be recorded as a function of wavelength or wavenumber. The sample area is designed to permit temperature and pH control and use of an automatic titration assembly. A three quartz plate beam splitter produces two identical beams (within 0.5%) over a range of 280 to 600 mμ, regardless of the polarization of the incident beam, thus allowing the measurement of accurate corrected excitation spectra. Total stray light present at exciting wavelengths from 210 to 240 mμ was measured: it amounted to 7% at 240 mμ. Polarization spectra (excitation as well as emission) can be measured continuously without altering the apparatus; a discriminator was built which separates two normally polarized components. Degree of polarization can be obtained within 1%, and this figure can be further improved by correcting for imperfect discrimination of the two polarized components. Corrections for light source fluctuations and nonlinearities as a function of wavelength and continuous polarization measurements are effected by a digital ratio system which allows unlimited time integration and has an infinite dynamic range. The long range drift introduced by this system and the photomultiplier current preamplifiers is below 0.03%. The limit on overall stability is determined by the photomultipliers, and amounts to 0.5% over the long range (due to gain variations).
Fast Neutron Time-of-Flight Spectrometer Used with the Karlsruhe Isochronous Cyclotron
Authors: Cierjacks S. , Duelli B. , Forti P. , Kopsch D. , Kropp L. , Lösel M. , Nebe J. , Schweickert H. , Unseld H.
Published: February 2004

A high resolution, fast neutron, time-of-flight spectrometer used for neutron energies between about several hundred kiloelectron volts and 30 MeV is described. A 1 nsec neutron pulse occurring with a repetition rate of 20 kc is obtained with a novel ``bunching deflection'' system operating on the internal beam of the fixed energy Karlsruhe isochronous cyclotron. By the timing of the neutrons over a 57 m flight path a resolution of 0.025 nsec/m at optimum was obtained. Detector counts are accumulated in a 2×8000 channel time analyzer system with 1 nsec channel width. A planned flight path of 180 m and an increase of the repetition rate from 20 kc at present to 200 kc is expected to provide further improvements of the spectrometer.
Automatic Multiparameter Data Collection
Authors: Green P. J. , Williams R. E. , Tompkins D. R.
Published: February 2004

A system which digitally analyzes multiple simultaneous voltage pulses is described in detail. The system uses a pulse height analyzer with paper tape readout. Simultaneous voltage pulses are stored to allow sequential analysis and routing to memory subgroups of the analyzer. Immediate memory readout accomplishes simultaneous pulse correlation with the memory address identifying the parameter number and pulse height. The single address in each memory subgroup storing a ``1'' is punched which minimizes the tape readout per event and allows tape storage of several thousand events. The dead time is 2nt where n is the number of memory channels of the analyzer and t is the readout time per character. Although the deadtime (approximately 7 sec for a 200 channel analyzer with a 60 character/sec punch) limits the system's use to low count rates, a suggested improvement is included which reduces the deadtime to 3n′t where n′ is the number of parameters to be recorded (0.21 sec for 4 parameters with a 60 character/sec tape punch).
Effect of Valve Opening Time on Gas Gun Performance
Authors: White Richard W. , Fowles Richard
Published: February 2004

In a light-gas gun a valving device introduces the high pressure gas from the breech into the barrel. For a particular gun design a 25% decrease in projectile velocity is predicted when the opening time of such a valving device is increased from 1 to 50 msec.
Temperature Controller for LEED Experiments
Authors: Tracy J. C.
Published: February 2004

A controller is described that enables the establishment of sample temperature as a function of time or some other experimental variable. It is well suited for electrically heated samples such as those used in low energy electron diffraction (LEED) experiments. The system is simple, easy to construct, inexpensive, and reliable. The LEED pattern is blanked synchronously with the heating current, allowing pattern observation during heating. This feature alone permits many previously impossible experiments to be performed.
One Thousand Meter Laser Interferometer
Authors: Vali V. , Bostrom R. C.
Published: February 2004

To provide high sensitivity and to observe a representative sample of the earth's surface, a laser extensometer having a length of 1020 m has been built and is in operation. The sensitivity of the instrument described is at present about Δl/l≅6 × 10−12.
Dual Mode Microwave Cavities for Dispersion Measurement
Authors: Thompson M. C. , Vetter M. J.
Published: February 2004

A technique has been developed for making precise measurements of refractive index dispersion in gases. The instrument, termed ``dispersometer,'' uses a cavity resonating in two modes simultaneously to measure the difference in index at two frequencies. Since the gas sample is common to both modes, effects of variations in gas pressure, temperature, and composition between samples are removed. In an early model, the precision of the measured dispersion was a few parts in 108 (of refractive index). The method has been used to date for a study of the 0.74 cm−1 water vapor line (reported separately) and should be equally applicable to other spectral regions, limited only by the available generation and detection devices.
Digital Time Intervalometer
Authors: Nutt Ronald
Published: February 2004

A digital time intervalometer was developed for measuring time intervals of 1 msec or less with a time resolution of ∼200 psec. The start signal can be delayed from 50 nsec to the full range of ∼1 msec. The range of the instrument is independent of the selected delay and can be set to cover intervals from 100 nsec to ∼1 msec. The instrument is unique in that analog time expansion is used to measure very accurately the time phase between a 20 MHz oscillator and the start and stop signals.
Live-Timer Method of Automatic Dead-Time Correction for Precision Counting
Authors: Porges K. G. , Rudnick S. J.
Published: February 2004

Several applications of live-timer count correction are discussed with regard to the precision and statistical accuracy of results obtained. The method is compared to conventional real-time operation with subsequent formula correction. For straightforward high-precision counting, the live-timer method is believed to be superior. Counting of sources which decay appreciably during the count, sometimes thought to be a case where automatic live-timer correction fails, can be accomplished by choosing a certain readily calculable ratio of clock inhibit duration to paralysis. Similarly, coincidence counting with different channel paralyses is found to be amenable to live-timer correction, with a resulting precision which exceeds that of formula corrections.
Magneto-Optical Method for the Measurement of the Spin-Lattice Relaxation Times of Paramagnetic Ions
Authors: Giltner Beverly S. , Lysiak Richard J.
Published: February 2004

A magneto-optical method has been developed to determine the spin-lattice relaxation times of paramagnetic ions from the maximum rate at which paramagnetism can follow an ac magnetic field modulating a dc magnetic field of 0–6000 G. The spin-lattice relaxation time τ of the paramagnetic ion determines the maximum rate at which the Faraday rotation of plane polarized light traversing the material may be modulated at low temperatures. By measuring the phase angle between the light modulated by the Faraday rotation and the perturbing magnetic field for both the pure host material and the host material doped with paramagnetic ions, one is able to determine the relationship between τ and the applied static magnetic field at low temperatures. The apparatus and the method employed for this measurement are described.
Precision Thermometer for the Region 10–40 K
Authors: Gill D. , Kaplan N. , Thompson R. , Jaccarino V. , Guggenheim H. J.
Published: February 2004

A low temperature thermometer based on the temperature dependence of the vF(T) of the 19F NMR frequency in antiferromagnetic MnF2 has been successfully operated in the 10–40 K temperature region. Novel features include the use of a MnF2 crystal with a sharp 19F NMR line as the temperature sensitive element in a solid state frequency-locking autodyne circuit that operates while completely submerged in liquid H2 or He. In the present design the circuit-sample combination takes the form of a compact probe. With this device temperature readings which are reproducible to ±10−4 K at 20 K have been obtained. Various applications for precision thermometry in the 10–40 K range using the device are proposed.
CO2-Laser Interferometer for the Measurement of Transient Low-Density Plasmas
Authors: Herold H. , Jahoda F. C.
Published: February 2004

A coupled cavity CO2-laser interferometer is described. The feedback is achieved either with (a) a rotating corner mirror or (b) an oscillating mirror. For method (a) a sensitivity of ∫ndl≥5×1014cm−2 and time resolution of 0.2 μsec is obtained. Method (b) is more sensitive (∫ndl≥1013cm−2) but the time resolution is limited by the fact that signal amplitudes are strongly frequency dependent above 350 kc. The interferometer has been used to measure plasma densities of the Scylla IA θ pinch.
Simple, Inexpensive Liquid Helium Temperature Controller, Using Integrated Semiconductor Circuits
Authors: Venegas Carlos M. , Finegold Leonard
Published: February 2004

We describe a controller for regulating the temperature of a pumped liquid helium bath. The controller is a considerable improvement over previous controllers in that it is much simpler and less expensive. These improvements are due mainly to an uncommon direct-coupled alternating current circuit, and to extensive use of the recently introduced integrated semiconductor circuits. The controller operates by measuring the resistance of a carbon radio resistor immersed in the liquid helium bath, and then feeding back a proportional correction current to a heater. The controller will control a bath to within 100 μK over a period of 20 min, at 2.1 K, and could be used to control the temperature of a copper block over a wide range of temperatures.
True Random Ratemeter with Automatic Dead-Time Correction for Duty Factors up to 99%
Authors: Metz A. J. , Howard R. H.
Published: February 2004

A true random ratemeter which automatically corrects for dead time is described. The unit requires two inputs: the normal pulse input and a signal whose duration equals the dead time of the channel being monitored. Variations in dead time, whether they are random or not, are automatically accommodated. Accuracy is 1% on all ranges even at duty factors up to 99%.
Rocket-Borne Rayleigh Scattering Instrumentation to Measure Atmospheric Density
Authors: Howlett L. C. , Swigart J. I.
Published: February 2004

A rocket-borne system to measure air density by detecting Rayleigh-scattered light from an onboard light source is described. The system utilized a high intensity mercury arc lamp to produce a modulated light beam. Light scattered from air molecules in a portion of the light beam beyond the disturbances caused by the sounding rocket was viewed by an optical system. The light receiver output was synchronously detected and telemetered to ground for analysis. Details of the instrumentation and flight results are discussed.
Mass Spectrographic Analysis of Silver Membrane Oxygen Leak
Authors: Burroughs E. G.
Published: February 2004

Mass spectra of evolved and diffused gases from a silver membrane oxygen leak have been obtained. Although the diffused gas was found to be almost exclusively oxygen, several important precautions were found necessary for its effective use, especially on sputter ion pumped vacuum systems.
A Pockels Cell Light Modulator for Wide Angle Radiation
Authors: Enemark E. A. , Gallagher Alan
Published: February 2004

A Pockels cell light modulator which operates at radio frequencies is described. It transmits more isotropic radiation than other Pockels cell or water cell modulators that operate at these frequencies. In addition, the modulated light has less phase variation between different components of the radiation than do water cell modulators.
Temperature Compensated Linearizer for Hot-Wire Anemometer
Authors: Kovasznay Leslie S. G. , Chevray René
Published: February 2004

A description of a ``linearizing circuit'' for low velocity hot-wire anemometry is given and a detailed analysis of the transistors chain used to generate the desired function is presented. The frequency response of the complete circuit proved very satisfactory, but special consideration had to be given to compensation for the temperature sensitivity inherent to solid state devices.
Radiographs of the Electron Beam Welding Cavity
Authors: Tong Henry , Giedt Warren H.
Published: February 2004

It has been suggested that a cavity is formed in the path of an electron beam and that this cavity accounts for the deep penetration capability of an electron beam welder. An experimental technique utilizing a high energy pulsed x-ray source was developed to obtain radiographs of the cavity during the actual welding process. These radiographs not only verify the existence of the cavity but also show that it oscillates in size and shape.
Temperature Insensitive Magnetostrictive Composites
Authors: Kench J. R.
Published: February 2004

Commercially available magnetostrictive composites employ the differential magnetostriction exhibited by materials of different composition and are therefore sensitive to temperature changes as well as to variations in magnetic field intensity. In order to overcome this problem a new approach has been adopted, using laminas of the same material which yet possess different magnetostrictive characteristics. It is shown how, by suitable choice of material, the laminas can be prepared from highly textured polycrystalline sheets so that one lamina contains a high proportion of 〈111〉 crystal directions along its length while the other contains mostly 〈100〉 crystal directions along its length. Such laminas are found to exhibit different magnetostrictive coefficients and may be bonded together to form an effective magnetostrictive composite which is inherently insensitive to temperature change.
A Double Beam Spectrophotometer for the Direct Measurement of Integrated Absorption Lines
Authors: Nicol Donald R.
Published: February 2004

A double beam spectrophotometer has been developed which uses a logarithmic amplifier to obtain absorption coefficients and the area under absorption curves. The wavelength range is from 3000 Å to 2.3 μ and resolution is determined by the grating monochromator to which the system is attached. With a resolution of 1 Å an absorption coefficient of 0.02 is easily measurable. The optical and electronic system of the instrument and its performance are described.
Low Temperature Thermometry in High Magnetic Fields. I. Carbon Resistors
Authors: Neuringer L. J. , Shapira Y.
Published: February 2004

Measurements of the transverse (sample current I normal to magnetic field H) and longitudinal (I∥H) magnetoresistance of 110, ⅛, and ¼ W Allen-Bradley carbon resistors were performed at various temperatures between 1.8 and 18 K in static magnetic fields up to 150 kG. Eleven different resistors having nominal values at room temperature of 47, 100, and 220 Ω were investigated. A description is given of a new technique which was devised to perform these measurements. The magnetoresistance of Allen-Bradley resistors is small, reproducible, and can be estimated from measurements on other resistors of the same nominal value. These resistors are useful, therefore, as thermometers in intense magnetic fields at low temperatures. A comparison is made between different empirical equations which have been used in attempts to fit the data. In addition, different methods are described for determining the temperature T and sensitivity R−1(∂R/∂T)H from the magnetoresistance data.
Measurement of Atomic and Molecular Beam Intensities with a Torsion Balance
Authors: Schmidt Conrad
Published: February 2004

Beam intensities of 1014 particles·cm−2·sec−1 are measured by a torsion balance with an accuracy of 3%. The sensitivity of the balance is 21.1 rad/dyne. In a dynamic mode the sensitivity can be increased by a factor of about 50. Accommodation coefficients need not be known.
The Pioneer 8 Cosmic Dust Experiment
Authors: Berg Otto E. , Richardson F. Frank
Published: February 2004

A cosmic dust sensor comprising a unique array of sensors, sensor controls, and in-flight calibrations was placed in a heliocentric orbit (0.99 to 1.088 a.u.) on 13 December 1967 on board the Pioneer 8 satellite. The ionization and momentum imparted by the impact of a cosmic dust particle upon a surface are measured by the sensor and used to determine the particle's direction, speed, and mass. Prelaunch calibration studies using the Goddard Space Flight Center electrostatic accelerator have shown that the sensors can measure kinetic energies of impacting particles as low as 0.6 ergs and momenta as low as 2×10−5 dynes·sec.
Rapid Scan Spectroscopy with a Refractor Plate as the Scanning Device
Authors: Roldan R.
Published: February 2004

A simple analysis is presented of the characteristics of a refractor plate as a scanning device for monochromators. The analysis shows that, although the scan produced by the refractor plate is not linear in time, an improvement can be obtained by using plates of high refractive index, and that optimum linearity is obtained for n=3.79. Further, it is shown that a resolution of better than 0.3 Å can be maintained over a 20 Å scanning interval by correcting for the defocusing effect of the refractor plate. The results are presented so that they can be readily used with any monochromator and refractor plate. The experimental measurements made with a glass plate (n=1.5) are in good agreement with the predictions of this analysis.
Highly Sensitive Capacitive Pressure Gauge
Authors: Straty G. C. , Adams E. D.
Published: February 2004

Two capacitive pressure gauges which have been used extensively in the study of liquid and solid helium are described. The first gauge, constructed of Be–Cu, has a sensitivity of Δp∼2×10−6 atm for pressures of 100 atm. It is highly stable, has essentially no hysteresis, and is affected very little by changes in temperature below 4.2 K. The second gauge is of nylon construction and is suitable for NMR or with paramagnetic salt thermometry. A detailed description of the construction and use of both gauges is given.
An Oven for a Neutron Spectrometer, to 1000 K
Authors: Bezdek H. F. , Schmunk R. E. , Finegold Leonard
Published: February 2004

A simple oven is described for keeping single crystal samples at high temperatures, for thermal neutron scattering work. Neutron transmission and reflection problems are solved, and sample temperatures can be held to a band of 2 K for several hours.
Mercury Lamp for Optical Pumping
Authors: Shernoff Donald I.
Published: February 2004

A small, electrodeless lamp has been developed which emits light at 2537 Å suitable for mercury optical pumping experiments. The light is intense, slightly self-reversed, and has a low noise level. The lamp, consisting of a 1 cm diam bulb containing argon and mercury, is excited by a 100 MHz transistor oscillator. The total power consumed by the circuit is 3 W.
Low Temperature High Sensitivity Temperature Compensated Heat Flux Sensor
Authors: Schulte E. H. , Kohl R. F.
Published: February 2004

Miniature (0.74×0.71×0.14 cm thick) heat flux transducers were designed and constructed to measure heat transfer by conduction, convection, radiation, or almost any combination of these from 75 to 300 K. A high sensitivity, approximately constant at 250 mV/(W/cm2), was obtained by utilizing the semiconductor silver-antimony-telluride. Temperature compensation was achieved by matching the changing properties of the insulating material to the changing properties of the semiconductor over the temperature range of interest. Data are presented on the comparison and selection of suitable materials for similar applications.
A Technique for Cutting and Polishing Small Metal Spheres
Authors: Gray W. J. , Spedding F. H.
Published: February 2004

A strain-free method for cutting spherical single crystals of metals and a method for polishing the rough spheres so obtained to nearly perfect sphericity are described. The polishing process introduces a small amount of surface strain, but this is easily and uniformly removed by a light electrical etch.
Measurement of Rapid Photoprocesses Using a Modulated cw Laser
Authors: Haug A. , Kohler B. E. , Priestley E. B. , Robinson G. W.
Published: February 2004

Spectroscopic techniques developed to investigate the kinetics of rapid photoprocesses occurring in the time domain 5×10−9 to 6×10−3 sec after excitation are described. The excitation system consists of a cw argon ion laser beam interrupted periodically at frequencies between 4 and 75 Hz by means of an electro-optic shutter. The shutter can be switched off within 3×10−8 sec and remains closed for approximately 6×10−3 sec, during which time the decay kinetics of the light emitted by the sample can be recorded by the detection system. The latter employs a fast photomultiplier and a sampling oscilloscope, the samples being stored digitally in a multichannel analyzer. Since an explicit decay curve is obtained from the measurements, no assumptions need be made about the form of the decay kinetics. Careful analysis of the data permits measurement of lifetimes that are much shorter than the time required to switch off the excitation light, the minimum being set by the signal-to-noise ratio alone. The use of signal averaging allows very weak signals to be measured and the emission decay curve to be followed accurately over several decades in time. Because steady state conditions are established during each cycle and the power density of the laser beam can conveniently be adjusted over the range from a few microwatts per square centimeter to several watts per square centimeter, this system is well suited to an investigation of fast photoprocesses in photosynthetic systems. The performance of the apparatus is illustrated by measuring the fluorescence decay from a solution of rubrene (5, 6, 11, 12-tetraphenylnaphthacene) in benzene. The measured lifetime is 16.3±2.1 nsec compared to a previously reported value of 16.42±1.15 nsec [J. Chem. Phys. 37, 814 (1962)]. Shortening of the lifetime due to the presence of impurities and oxygen in the solution is also discussed.
A Simple Mass Spectrometer
Authors: Dawson P. H. , Hedman J. W. , Whetten N. R.
Published: February 2004

A mass spectrometer of unusually simple construction is described. The three electrodes were hand formed from coarse stainless steel mesh. Despite the imprecise shape of the electrodes, the spectrometer has a half-height resolution of 75. The device is a three dimensional quadrupole, or ion trap type of mass spectrometer. It is operated so as to store a single m/e species at a time. After a suitable storage time, the ions are pulsed out of the trap into an electron multiplier for detection. The optimization of operating parameters and the ion buildup characteristics for various gases are presented. The performance of the instrument is compared to that of a magnetic sector mass spectrometer. The cracking patterns are simpler than for the magnetic analyzer. In contrast with the magnetic analyzer, no extraneous peaks due to ion desorption from surfaces are present. The lowest measured partial pressure was about 10−12 Torr, and this was limited only by the minimum total pressure attained. Trace analysis capability of 1 part in 2500 was observed with little effort to optimize this property.
Afterglow Plasma Diagnostics with a Microwave Sampling Radiometer
Authors: Stenzel R. L. , Gould R. W.
Published: February 2004

A simple waveguide arrangement has been developed for the study of microwave absorption and emission from a magnetized afterglow plasma column. The time and frequency resolved measurements are performed by a sampling radiometer. A comparison and null technique permits the direct measurement of the electron temperature. Continuous plots of the temperature vs frequency, magnetic field, and afterglow time are made possible by means of a servoloop. The width of the emission or absorption spectrum in the range of upper hybrid frequencies is used to derive the electron density which, together with the temperature measurement, allows a more complete analysis of the plasma decay.
A Light Pulse Demodulator with Large Bandwidth and High Sensitivity
Authors: Tyler Charles E.
Published: February 2004

A pulse demodulation technique is described which, by employing the zero crossing technique, enables one to avoid the usual photomultiplier bandwidth limitation imposed by the anode risetime. The sensitivity limitation imposed by the photoelectric quantum noise is automatically eliminated. A light pulse with 0.4 nsec risetime is demodulated.
Magnetic Field Uniformity around Near-Helmholtz Coil Configurations
Authors: Cacak R. K. , Craig J. R.
Published: February 2004

The magnitude of the total magnetic field in the vicinity of a single round coil pair, a single square coil pair, and a trio of mutually orthogonal round coil pairs has been computer calculated, and the results graphically displayed as a series of contour lines. An investigation of the uniformity of field as a function of coil spacing indicates a distinct optimum near the Helmholtz spacing.
Ceramic Plasma Container for Ion Lasers
Authors: Nasini M. , Pratesi R. , Redaelli G.
Published: February 2004

A very simple method for constructing ceramic plasma containers is described employing a low cost, commercial ceramic (Sintox) and the soldered seal technique. Discharge tubes for ion laser applications have been realized with operation characteristics comparable to those reported for beryllia tubes and the moly-manganese technique.
Extensions of Callendar's Equations for Platinum Resistance Thermometry
Authors: Diamond Joseph M.
Published: February 2004

Callendar's equations are generalized to permit interpolation between arbitrary fixed points. Fixed points appropriate to a desired temperature region may thus be employed, rather than Callendar's fixed 0 and 100°C calibration points. This should afford greater accuracy, especially in industrial measurements where the platinum thermometer and the measurement means may be less than ideal. To this end, Callendar's definition of platinum temperature is generalized to mean the temperature found by linear interpolation with a platinum thermometer between given fixed points and using a given measurement method. The true temperature may then be found either by recursion or by an extension of Callendar's correction scheme. It is shown that the effect of a general calibration interval T1, T2, rather than Callendar's 0 to 100°C interval, is to alter the effective value of δ in a calculable way. When deflection rather than balanced-bridge methods are used, it is shown that the effect of bridge nonlinearity may be approximated by an additional calculable alteration of δ.
Development and Application of a Spark Source for Multiply Charged Carbon Ions
Authors: Zwally H. J. , Koopman David W. , Wilkerson T. D.
Published: February 2004

A triggered spark source for C+, C2+, C3+, and C4+ ions has been built that yields ∼2 μsec duration bursts of ions with an energy per unit charge range of 50 eV to 10 keV. After charge separation and 4% energy selection 103−105 ions/pulse are obtained. The source is similar in design to titanium-washer hydrogen plasma guns, but in the present application graphite washers are used. Methods for overcoming experimental problems associated with this type of source have been developed and the source has been successfully used for collision experiments.
Measurement of Large Angle Atomic Scattering Using Axially Symmetric Magnetic Fields
Authors: Bush T. O. , Heinz O. , Rodeback G. W. , Cook C. J.
Published: February 2004

A technique using the focusing properties of a nonuniform axially symmetric magnetic field to study large angle (θ>32°, lab) scattering of ions from atoms and molecules is described. The scattering cell is placed on the magnetic axis at the position of maximum field and ions in the momentum interval |Δp| at |p| scattered into a conical shell Δθ at θ are counted by a detector placed down along the axis in a region of low field. The solid angle is increased by a factor of several hundred over conventional scattering techniques of comparable angular resolution due to the azimuthal symmetry of the apparatus. The magnetic vector potential and the trajectory equation for a charged particle in this type of inhomogeneous, axially symmetric field are derived. As a preliminary test the known differential scattering cross section for He+ on the He was measured from 40 to 52° (lab) at 300 eV. Results of measurements of the absolute differential scattering cross sections for Li+ on He from 36 to 41.7° at 200 and 300 eV, corresponding to CM scattering angles of 90 to 160°, are presented.
Spectroscopic Method for Simultaneous Determination of Species Concentration and Temperature in a Cyclic Combustion Process
Authors: Smith D. S. , Starkman E. S.
Published: February 2004

An optical method for the simultaneous determination of species concentration and temperature in a high pressure transient combustion and expansion process is described. The experimental system utilizes a mechanically chopped (2000 Hz) external radiation signal to perturb the self-emission signal from the combustion gas of an internal combustion engine. Distinguishing between the emission and absorption signals simultaneously provides a capability for determination of species concentration by absorption and of optical temperature by an emission-absorption technique.
Spherical Multipole Magnets for Plasma Research
Authors: Sadowski M.
Published: February 2004

Spherical multipole (SM) magnetic fields are used for plasma containment. Such magnetic fields are produced by magnetic dipoles symmetrically placed on the sides and the edges of regular polyhedrons. In the paper, field configuration of the high order SM systems is considered and some basic problems regarding the design of SM electromagnets are discussed. Relations are given relating magnetic field, power input, current- and temperature- time characteristics. The construction and operation of the ``Kaktus'' magnet are also described.
Low Temperature Thermal Conductivity of Several Greases
Authors: Kreitman M. M.
Published: February 2004

The temperature dependence of the thermal conductivity of silicone vacuum grease, Cry-Con grease (a copper loaded electrically insulating grease), and Eccotherm TC-4 (a specially formulated paste based on silicones and fillers) has been measured at liquid helium temperatures. It is concluded that the (thermal) greases examined have thermal conductivities in bulk corresponding approximately to those of thermal insulators. The successful use of thermal bonding greases to effect heat transfer at liquid helium temperatures and below requires very thin layers of the greases, in order to avoid the deleterious effect of their poor thermal conductivity in bulk.
Design and Analysis of a High Intensity Fast Oxygen Atom Source
Authors: Miller David R. , Patch Dan F.
Published: February 2004

A mixture of 5% O2 in He has been used in a rf discharge at pressures from 15 to 70 Torr to produce a free jet source of a high intensity energetic beam of atomic oxygen. Intensities of 1017 atoms/sec/sr are predicted and energies of 0.33 eV have been measured. A time-of-flight analysis of the beam properties is presented and indicates that the source temperature is near 620 K.
A New Type of Surface Ionization Detector
Authors: Politiek J. , Los J.
Published: February 2004

The ionization coefficient of a potassium atom impinging on a hot Pt-8% W wire is independent of its energy below 3 eV (3850 m/sec) and dependent on it above 3 eV. This is due to the fact that a high energy atom can reflect from the wire without being ionized. By using a tungsten cylinder as an ionizer and a niobium wire in the middle of it as a collector, incident atoms which are not ionized can be prevented from leaving the cylinder without being detected because subsequent collisions with the wall will take place and result in ionization. By means of this type of standard detector, which has a multiplication factor of about 30, the reflection coefficient of a potassium atom incident on a Pt-8% W wire is determined as a function of its velocity. For a potassium atom with an energy of 23.6 eV (10 800 m/sec) this reflection coefficient is about 16.5%.
Calorimeter for Simultaneous Measurements of Stored Energy and Resistance
Authors: Ryan E. A. , Jackson J. J.
Published: February 2004

An adiabatic calorimeter using digital data acquisition and programmed heating for measurement of stored energy in the range 350–1000 K is described. In addition to combining the advantages inherent in digital acquisition systems with the advantages of an adiabatic calorimeter, samples were heated by Joule heating permitting (1) simultaneous measurement of stored energy and resistance and (2) calibration of the system including losses. This arrangement, when applied to measure the stored energy and resistance associated with defects introduced in samples by quenching, plastic deformation, or radiation damage, has sufficient sensitivity not only to measure the total stored energy but also to yield a spectrum of the energy release as a function of temperature. Calibration data indicated that energy release rates as small as 10 μW could be measured. Measured losses which were nearly independent of temperature totaled approximately 5.5 μW. Resistance measurements were reproducible to better than 10 parts in 10.6
Microwave Helices in Electron Spin Resonance Studies at High Pressure or Very Stable Temperatures
Authors: Plachy William Z. , Schaafsma Tjeerd J.
Published: February 2004

Special purpose ESR systems which make use of helical slow wave devices are described. One such system can be used to study liquids at pressures in excess of those employed in ordinary cavity systems. An ESR cell with temperature fluctuations and gradients of less than 10−3°C is also described.
The Effect of Variable Fluid Properties on the Sensitivity of MHD Flowmeters
Authors: Thomson William J. , Bopp Gordon R.
Published: February 2004

For ducts operated as MHD flowmeters, it is demonstrated that the sensitivities are substantially affected by variable fluid viscosity and electrical conductivity. The analysis considers a mathematical model based on fully developed laminar MHD flows with constant heat flux boundary conditions. By considering the pertinent equations in dimensionless form and assuming a power law dependency of the fluid properties on temperature, flowmeter sensitivities are calculated as functions of the Hartmann number, duct aspect ratio, and the magnitude of the property variations. It is shown that, even for small property variations, the flowmeter sensitivities deviate significantly from constant property values. For larger variations, they can be as much as 60% below ideality for heated walls and 30% above for cooled walls.
Rotatable 15 kOe Superconducting Helmholtz Coils
Authors: Williamson S. J.
Published: February 2004

A pair of superconducting coils in an approximate Helmholtz configuration is described which is capable of producing a magnetic field intensity in excess of 15 kOe with a homogeneity of ±0.1% within 0.5 cm of the field center and ±1.0% within 1.5 cm. The pair is mounted and geared so as to produce a horizontal field whose direction can be rotated 360° about a vertical axis. The magnet assembly has a 2.90 cm diam vertical access hole for a sample mount and can be accommodated within a 12.7 cm i.d. Dewar.
Carrier Gas Diverting Apparatus for Flame-Fusion Crystal Growth
Authors: Adamski Joseph A.
Published: February 2004

A device for diverting the flow of a carrier gas from the normal flow pattern of a conventional Verneuil apparatus has been fabricated and used. This improved carrier gas assembly provides a means for replenishing powder feed material or substituting an alternate material without disturbing crystal growth environment or disrupting the growth of unusually long crystals. The temperature of the growing crystal, and the liquid-solid crystal growing interface remain stable during these operations.
Single Crystal Transfer Device and Rotation System for ESR Measurements
Authors: Hornyak E. J. , Beem K. M. , Rasmussen P. G.
Published: February 2004

A device has been designed for the transfer and rotation of single crystals so that angular dependent ESR data can be obtained with a stationary magnet and rectangular cavity. The apparatus consists of a modified Donnay optical analyzer and a second goniometer which is rotated about a vertical axis in the ESR instrument. It has been possible to transfer crystals within ±0.5° of the desired orientation. Measurements of effective g values on two systems yielded standard deviations of 0.001 or less.