bluuebunny/crossref_metadata_2025 huggingface dataset:
An Energy Modulated High Energy Resolution Electron Spectrometer
Authors: Golden D. E. , Zecca A.
Published: February 2004

A new cylindrical retarding potential difference type or energy modulated electron spectrometer has been constructed with high energy resolution. For energies greater than 1 eV the ratio of beam current I to energy spread FWHM, ΔE has been found to be approximately constant so that I/ΔE≃10−7 (A/eV) at about 20 eV. For electron energies from 0 to 1 eV the electron current increases with energy by about 10−7 A/eV for ΔE≃0.1 eV to the value given by the above expression. For energies above 1 eV the electron current is a very slowly varying function of energy. The energy resolution has been checked to 0.008 eV by studying the shape of the He−(2S½) resonance at 19.3 eV in a transmission experiment. The over-all performance of the spectrometer has been studied for electron energies from 0 to 60 eV in transmission experiments in He by studying structures in the electron scattering cross section.
Accurate Calibration of Philips EM300 Electron Microscope Goniometer Stage Double-Tilt Holder
Authors: Pumphrey P. H. , Bowkett K. M.
Published: February 2004

A method is described for the accurate calibration of electron microscope tilting holders. Diffraction patterns taken from a specimen as it is tilted can be accurately analyzed and used to calibrate the tilt angle and axis of the holder. The method is applied to a test of the double tilt holder of a Philips EM300. The tilt axis is shown to change by about 8° as the specimen is tilted from −30 to +30°.
Coaxial Cell for Liquid Dielectric Measurements from 300 to 9000 MHz
Authors: Payne Richard , Theodorou Ignatius E.
Published: February 2004

The dielectric constant and loss of a liquid dielectric are determined from measurements of the input impedance of a coaxial cell terminated with a short circuit. The location of the short circuit is continuously variable over a range of 2.5 cm to allow selection of the optimum sample length. Dielectric constants from 1 to 100 with high or low loss have been measured in the frequency range 300–9000 MHz using the General Radio type 900LB slotted line.
Application of the Birnboim Multiple Lumped Resonator Principle to Viscoelastic Measurements of Dilute Macromolecular Solutions
Authors: Schrag John L. , Johnson Robert M.
Published: February 2004

A new multiple lumped resonator apparatus for the measurement of the viscoelastic properties of very dilute macromolecular solutions is described. The instrument may be used to study the viscoelastic behavior appropriate to infinite dilution for comparison with current theories. It has a frequency range from 100 to 8300 Hz (discrete frequencies) and may be used with solution viscosities from 0.005 to 0.5 P. Values of G′ less than 0.5 dyne/cm2 have been measured with reasonable accuracy when used in conjunction with a computerized data acquisition system.
The Magnetic Susceptibility and Specific Heat of Constantan at Low Temperatures
Authors: Yee R. , Zimmerman George O.
Published: February 2004

The magnetic susceptibility of constantan has been measured in the temperature region between 1 and 0.033 K, and its specific heat between 1 and 0.76 K. Both measurements give evidence of a phase transition near 0.76 K. In addition we find a susceptibility anomaly near 0.08 K which is associated with a previously reported specific heat maximum.
A Generalized Pulse Height Distribution for the Electron Multiplier
Authors: Wright W. H.
Published: February 2004

The generalized birth and death process is used as a model for the creation of secondary electrons in order to obtain the pulse height distribution of an electron multiplier. A recurrence relation is obtained for the distribution Pk(n) of the total number n of secondaries after k stages of multiplication, which result from a single electron input. It is possible to use different birth and death functions at each dynode. Results are presented using birth and death functions based on an elementary but physically meaningful theory of the secondary emission process.
Modification of High Resolution Mass Spectrometer for Chemical Ionization Studies
Authors: Futrell Jean H. , Wojcik Leonard H.
Published: February 2004

The additional instrumentation and several modifications required to permit operation of a Consolidated 21–110B mass spectrometer at source pressures of the order of 1 Torr are described. A spark suppressor system was devised to permit operation of the ion source at potentials to 10 kV while the sample handling and pressure measuring equipment are maintained at ground potential. Several circuit modifications necessary for high pressure operation are also described. All changes are compatible with the use of standard components for sample manipulation and with the consecutive use of the ion source for low pressure electron impact and high pressure chemical ionization mass spectroscopy. A resolving power M/ΔM of 56 700 is demonstrated for the instrument, illustrating that the performance is not degraded by high pressure operation. The sensitivity and quantitative accuracy already achieved are comparable to conventional electron impact spectroscopy, while the spectra themselves are greatly simplified.
Sensitive Fast Response Electron Detector
Authors: Kuswa Glenn W.
Published: February 2004

A miniature scintillation electron detector was developed for use with a small energy analyzer working in the range of 0.5–1000 eV. The gain was 104, and the inherent risetime was ∼5 nsec, given sufficient input signal. Optical coupling of the signal eliminated ground loops.
An Apparatus for the Study of Rapid Phase Transformation Kinetics in Metals
Authors: Ayers J. D. , Barnes W. C.
Published: February 2004

An apparatus is described which makes possible kinetic studies of phase transformations which occur in metals within times as short as a few milliseconds. The apparatus consists of a capacitor discharge heating unit together with electronic circuitry which permits quantitative kinetic measurements during transformations which produce only small resistivity changes. The small voltage changes produced by the transformations are resolved by differentiating out the dc component of the signal and then integrating the output of the differentiator. Measurements are made on the integrator output, which contains only the ac component of the original signal.
Electron Beam Technique for Measuring Microvolt Changes in Contact Potential
Authors: Steinrisser F. , Hetrick Robert E.
Published: February 2004

A low voltage electron beam technique is reported which when coupled with ac detection is capable of measuring periodic changes in contact potential as small as 1.0μV. This sensitivity, which exceeds by a factor greater than 100 the reported sensitivities obtained by other methods, should enhance the usefulness of the contact potential measurement for detailed surface studies, especially in the case of semiconductors. The potential of the technique is demonstrated in the context of high resolution photovoltage measurements in n-type CdS which may allow for a sensitive form of surface state or surface barrier spectroscopy.
Metastable Atom Probe for Measurement of Electron Beam Density Profiles
Authors: Lockhart James M. , Zorn Jens C.
Published: February 2004

A well collimated thermal beam of argon atoms, moving in the z direction, crosses the electron beam that is to be studied. Those argon atoms that are excited by impact to a metastable state proceed, with very little change in speed or direction, to a detector (windowless electron multiplier) some distance away. The neutral atomic beam of the metastable atom probe (MAP) has a negligible interaction with the electromagnetic fields that govern the behavior of the electron beam; moreover, almost no additional space charge is created when the atomic beam is introduced. Thus, if the cross section of the atomic argon beam is small compared to the characteristic dimensions of the electrode structure that defines the electron beam, the metastable atom count rate, monitored as a function of x and y, gives a virtually nonperturbative measurement of the density profile of the electron beam. In this paper we outline the principles and applications of the method, discuss details of its implementation, and give results obtained with an MAP that has a spatial resolution of better than 0.5 mm.
Thermal Conductance Measurement in Electroexplosive Devices by Self-Balancing Bridge Techniques
Authors: Rosenthal Louis A.
Published: February 2004

An electroexplosive device installed as one arm of a self-balancing bridge will yield a measurement of the thermal contact between the bridgewire and the explosive environment. This thermal conductance measurement can be used as a basic design or quality control parameter.
Automated Chemical Synthesis Controlled by Computer Generated Programs-Polypeptides
Authors: Tometsko A. M. , Garden J. , Tischio J.
Published: February 2004

Instrumentation for the automated chemical synthesis of polypeptides controlled by computer generated paper tape programs is described. The automatic chemical reaction system (ACRS) translated binary coded commands from the paper tape into physical operations resulting in the synthesis of a model polypeptide. The commands for the entire synthesis were generated by computers. Using our computer programs for the synthesis of polypeptides, it is necessary only to specify the amino acid sequence and the computer will set up the appropriate sequence of physical operations (wash cycles, stirring, filtration steps, amino acid additions, etc.) to carry out the synthesis of the desired amino acid sequence. The computer could also automatically make adjustments in the synthetic approach to accommodate the unique problems involved in coupling different amino acids.
Application of a Differential Interferometer to the Measurement of Heat Transfer Coefficients
Authors: Black W. Z. , Carr W. W.
Published: February 2004

The basic components and principles of operation of a differential interferometer are discussed. This type of interferometer is inexpensive, relatively insensitive to vibration, and does not require extensive alignment adjustments. For free convection to an ideal gas the differential interferometer produces a fringe shift that is a function of the temperature gradient. The interferometer described is capable of producing an infinite fringe pattern in which fringe lines correspond to lines of constant index of refraction gradient. These facts make the differential interferometer useful for the measurement of convective heat transfer coefficients and flow visualization, particularly in dynamic systems and in cases where there are rapid fluctuation in the flow structure. A derivation of an expression for the free convection heat transfer coefficient is presented as a function of fringe shift. Several interferograms are included.
An Experimental Arrangement for the Observation of Light Scattering by Polaritons
Authors: Claus R.
Published: February 2004

Experimental problems concerned with observation of Raman scattering by polaritons are discussed. An arrangement allowing the observation of scattering processes in parallel planes is described. The method proved to be very useful in order to avoid disturbing effects owing to anisotropy. Spectra of the upper polariton region of LiIO3 are shown in order to demonstrate the arrangement.
Nondispersive X-Ray Spectrograph for Analysis of Light Elements down to Beryllium
Authors: Schoenfeldt D. , Pluchery M.
Published: February 2004

A nondispersive x-ray spectrograph, using an x-ray tube of the Henke type as the excitation source and a proportional counter as the detector, allows the analysis of light elements down to Be.
A Chemical-Stop Rapid Flow Apparatus
Authors: Lymn Richard W. , Gibson George H. , Hanacek John
Published: February 2004

A rapid flow apparatus with multiple mixers is described, capable of measuring reaction times of 0.008 to 0.5 sec. The solution-containing parts are of Teflon and Lucite to minimize metal contamination. A rack and pinion drive, using an electric clutch, is described, along with a positive assay valve needed when the apparatus is used as a chemical-stop flow apparatus.
A Sensitive Linear Capacitance-to-Voltage Converter, with Applications to Surface Wave Measurements
Authors: McGoldrick L. F.
Published: February 2004

A small size, low power demand, inexpensive device to convert fluctuating capacitance to linearly fluctuating voltage is described. An application of this device to surface wave measurements is made following a description of several transducers for converting fluctuating wave heights to a linearly fluctuating capacitance.
High Resolution Electron Tunneling Spectroscopy
Authors: Adler J. G. , Chen T. T. , Straus J.
Published: February 2004

A system which is capable of resolving changes in a tunneling junction conductance σ of about one part in 105 as well as providing calibrated values of dσ/dV is described. Methods of simultaneous analog and digital recording on magnetic tape suitable for subsequent computer analysis are given. The flow chart for the computer programming is also presented along with a typical result.
Apparatus for Measuring the High Temperature Strength of Filaments
Authors: Veltri Richard D. , Galasso Francis
Published: February 2004

One apparatus is described for measuring the high temperature tensile strength of metallic fibers and another one for measuring the strength of single carbon filaments. Typical results are given for tungsten filaments up to 1000°C exposure and for graphite filaments up to 500°C.
Automatic Control of the Drifting Process for Semiconductor Radiation Detectors
Authors: Erramuspe H. J. , Sinderman J. E.
Published: February 2004

An automatic Li drifting apparatus is presented which controls the temperature of the detector bath to maintain the leakage current at a preselected value. When the Li ions reach the back of the wafer the temperature is automatically reduced to room temperature, leaving or not, optionally, the bias voltage applied. The need for constant supervision is therefore eliminated.
Design and Construction of Multiring Apparatus for Use at High Pressures
Authors: Venkatesan P. S.
Published: February 2004

A pressure vessel providing more efficient use of constituent material for containing fluid pressure is based on a multiring assembly wherein the interferences between adjacent rings are chosen so that at all radii, except the last, the working stresses are made equal to each other and made equal to a predetermined value. The design equations are solved by a computer program employing various bore pressures in a 2.54 cm diam chamber using different working stresses and ratios of thickness to inside radius of ring segments.
A Discussion of the Region of Linear Operation of Photomultipliers
Authors: Land Peter L.
Published: February 2004

A theoretical analysis shows factors which affect the onset of nonlinear response of the anode current of a photomultiplier to the light intensity incident on the photocathode, when the dynode voltages are provided by a linear resistor chain. The percent deviation from linearity of the anode current is shown to be independent of the number of dynodes and the gain per stage. The conditions do depend on the form of the gain per stage which is assumed to depend on parameters g=p+q. The parameter g is shown to have approximately the same value for a number of photomultipliers, so that any significant differences in the initial deviation from linearity would be attributed to the ratio p/q. This ratio has not been measured, but a method of doing so is described. Some measurements of the deviation from linearity are discussed in terms of the analysis, and the indications from that limited sampling are that one can expect deviations to be less than 3% for all photomultipliers when the anode current is less than 0.1 the current in the final resistor of a linear bleeder chain.
An Apparatus for Shearing Bulk Materials at High Temperature, High Pressure, and Various Strain Rates
Authors: Abey A. E. , Dibley L. L. , Joslyn E. D. , Stromberg H. D.
Published: February 2004

An apparatus is described which measures the shear strength of bulk materials in the temperature range from 25 to 350°C, in the pressure range from 20–80 kilobars. The strain rate in this pressure and temperature range can be varied between 3.5×10−7 and 3.7×10−1 sec−1. Some data on OFHC copper are given to indicate the type of results obtained from this apparatus.
An Optical Magnetometer for Superconductivity Measurements
Authors: Griffiths David J.
Published: February 2004

The magneto-optical Faraday effect associated with certain paramagnetic ions has been utilized to construct an optical magnetometer suitable for studying the magnetic properties of hollow cylinder superconductors. As an instantaneous field detector, the response of the system in general is limited only by the spin-bath relaxation time of the paramagnetic ion-host crystal system being used. The magnetometer has the advantage of requiring no moving parts and also avoids the necessity of having to extract a low level voltage signal from the low temperature environment. Also, since the detector is an insulator, there are no undesirable time derivative of field signals generated in its use. The operating field range is limited by the sensitivity desired in a given experiment. For fields up to 13.5 kOe at a temperature of 2.15 K, the sensitivity for the analyzer oriented at 45° with respect to the plane of polarization of the emergent light is at worst ±9.3 Oe. The text lists the sensitivity at various other fields and temperatures in tabular form. Initial results on superconducting hollow cylinder niobium are also presented.
A Rotary Molecular Effusion Source for High Temperature Vaporization Studies
Authors: Muenow D. W. , Grimley R. T.
Published: February 2004

A high temperature rotary Knudsen cell assembly is described which, operating in conjunction with a mass spectrometer, may be used to determine the spatial distributions of individual species effusing from ideal and nonideal orifices and of species vaporizing from surfaces. This unit rotates about an axis contained within the plane of the face of the orifice or surface and is capable of reproducible angular settings of 0.2° under high temperature, high vacuum conditions. The apparatus is particularly suited to those types of mass spectrometers which are too cumbersome to be used as movable detectors. The angular distribution curves which result from these measurements may be used to determine orifice transmission probabilities and, in certain cases, to determine mass spectrometric parent-fragment relationships which other techniques have failed to resolve.
Nuclear Resonance Spectrometers Using Field Effect Transistors
Authors: Sullivan Neil
Published: February 2004

We describe the use of field effect transistors of both the metal-oxide-semiconductor and the n-channel junction type in marginal oscillator circuits designed respectively for the observation of NMR in the range 2–60 MHz and NQR in the range 3–40 MHz.
The Preparation of Large Plastic Films for Proportional Counter Windows
Authors: Grader R. J. , Hill R. W. , McGoff C. W. , Salmi D. S. , Stoering J. P.
Published: February 2004

The preparation of thin and uniform plastic films for rocket-borne x-ray proportional counters is described. The technique has produced entrance windows of 60 μg/cm2 thickness and 700 cm2 in area.
A Self-Detecting Microwave Marginal Oscillator
Authors: Walsh W. M. , Rupp L. W.
Published: February 2004

A very simple and compact 12 GHz marginal oscillator employs a commercial Gunn device as both microwave source and detector. The sensitivity to electron spin resonance absorption (3×1012 standard spins) is comparable to that of a conventional homodyne bridge spectrometer. As a heterodyne detector of externally generated microwaves the sensitivity is ∼10−12 W.
Oxidation Apparatus for Determining Rates of Oxygen Absorption of Lubricants
Authors: Dotterer G. O.
Published: February 2004

An oxidation apparatus is described which continuously records the volume of oxygen absorbed by a sample of oil, in a closed system, maintained at constant temperature and pressure. The apparatus is automated through the use of a specially devised liquid level probe and other ancillary equipment such as recorders, timers, and temperature controllers. The apparatus can be used to compare the relative oxidation stability of various lubricants over a wide range of operating conditions.
Development of a Compton Polarimeter with Solid State Detectors
Authors: Hardy K. A. , Lumpkin A. , Lee Y. K. , Owen G. E. , Shnidman R.
Published: February 2004

A two-section Compton polarimeter has been developed out of a single Ge–Li detector. This device has nearly the same asymmetry ratio as the three-section polarimeter described previously, but has the advantage of a high efficiency. The asymmetry ratio of the device is calculated as a function of gamma ray energy. The polarimeter is also calibrated by gamma rays of known polarization from reactions 24Mg(p,p′) and 28Si(p,p′).
A Single Sideband Interferometer for the Measurement and Control of a Velocity Transducer
Authors: Eylon S. , Treves D.
Published: February 2004

A method for the measurement and control of the velocity of moving objects using a single sideband interferometer (SSBI) is described. The method is applied to a Mössbauer spectrometer velocity transducer. The performance of the system operating between −1 and +1 cm/sec at constant velocity was measured. The long term mean velocity stability was 0.003 cm/sec. Instantaneous velocity ripple was less than 0.001 cm/sec.
Studies of a Glass-Ceramic Capacitance Thermometer between 0.025 and 2.4 K
Authors: Lawless W. N. , Radebaugh Ray , Soulen R. J.
Published: February 2004

Capacitance measurements from 0.025 to 2.4 K are reported for capacitance thermometers (made from an SrTiO3 glass-ceramic crystallized at 1100 and 1203°C), two of which were the ones reported in the previous article. It was found that the 1200-type thermometer has a useful thermometric range down to 0.06 K and a linear C-T region down to 0.5 K. The 1100-type thermometer has a useful range down to 0.110 K and a linear region down to 1.1 K. The measured data do not appear to be influenced by self-heating or adiabatic correction effects. Both thermometers display an unexpected increase in capacitance with decreasing temperature below their monotonically decreasing ranges. The 1100-type thermometer displays the more pronounced increase, with C∝T−1 from 0.100 to 0.025 K. It is argued that this T−1 behavior is due to the onset of an ultralow temperature phase transition in the glass crystallized SrTiO3, and the possibility of using this effect to achieve adiabatic depolarization cooling is discussed.
Measurement of the Thermal Pressure Coefficient (∂P/∂T)v of Molten Salts
Authors: Cleaver B. , Neil B. C. J. , Spencer P. N.
Published: February 2004

A method for the determination of the thermal pressure coefficient (∂P/∂T)v or γv for molten salts up to 400°C and 400 bars is described. The results, which are considered to be accurate to ±3%, are compared with previous work.
Refrigerating Vapor Bath
Authors: Puckett L. J. , Teague M. W. , McCoy D. G.
Published: February 2004

A simple and inexpensive refrigerating vapor bath has been developed for the purpose of cooling gas line traps. The cooling medium in the bath is the cold vapor from liquid nitrogen. The temperature regulation range is from −196 to ∼0°C. For a glass-isolated stainless steel gas trap the liquid nitrogen consumption rate was less than ½ liter/24 h at temperatures between −130 and −196°C.
A Comparison of Ta, W, and Pt-8%W Surface Ionization Detectors for Fast Potassium Atom Detection
Authors: Cuderman J. F.
Published: February 2004

Data are presented which describe and compare the behavior of Ta, W, and Pt-8%W surface ionization detectors for fast potassium atom detection. The potassium atom energy in these experiments covered the range from thermal energy to 500 eV.
A Low Cost Versatile Arc Melter
Authors: Cadieu F. J. , Cooley L. F. , Douglass D. H.
Published: February 2004

We have designed and built an arc melter which uses an inexpensive Pyrex pipe cross for a controlled atmosphere chamber. An argon jet has been incorporated into the electrode holder which provides both dynamic flushing and rapid quenching capabilities.
Corona Discharge Anemometer and Its Operational Hypothesis
Authors: Desai Prateen V. , Johnston William C.
Published: February 2004

The paper presents an outline of the physical mechanism of corona discharge between a highly stressed anode and a large plate cathode as applied to the operation of a new type of anemometer. An operational hypothesis is proposed for the anemometer with reference to its kinematic and electrostatic principles of performance. Experimental results are presented to justify the hypothesis and the calibration of the probe. A discussion of the probe sensitivity to yaw of gas stream is included.
Resistance of a Silicon Bronze at Low Temperatures
Authors: Sullivan D. B.
Published: February 2004

A specially prepared silicon bronze is shown to be quite insensitive to magnetic field and temperature change at liquid helium temperatures. The temperature coefficient of resistance is of the order of a few parts per million per degree over the range 2–10 K and the change in resistance at a flux density of 1 T (104 G) is about 10 ppm.
Polymers at Low Temperatures: Increasing Thermal Diffusivity in Specific Heat Measurements
Authors: Cude Jesse L. , Finegold Leonard
Published: February 2004

The thermal diffusivity of samples of powdered high polymers can be increased (at least in the temperature range 1–20 K) by compressing them with copper powder. Hence thermal relaxation times in specific heat measurements can be decreased. The specific heat of the copper is relatively small and is well known. Calorimeter vessels are then unnecessary.
Improved Method of Spinning Rotors to High Speeds at Low Temperature
Authors: Beams J. W.
Published: February 2004

A technique is described for spinning rotors of almost any size up to rotational speeds limited only by their strength, at liquid helium temperatures. The rotor is spun on the lower end of a long vertical stainless steel hypodermic needle tube shaft which connects to an air turbine drive above the apparatus. Electrical leads from the rotor are brought out through the hollow shaft and liquid mercury contacts. A convenient low noise system of liquid mercury electrical connections is described.
The Behavior of Type K Thermocouples in Temperature Measurement: The Chromel P-Alumel Thermocouples
Authors: Campari M. , Garribba S.
Published: February 2004

A study has been made on the origin of internal errors of type K and particularly of Chromel P-Alumel thermocouples. Physical and chemical nonuniformities fixed in the materials and subsequent modifications occurring in the system set a lower limit to the error band within which it is not legitimate to expect any better degree of accuracy. Effects of chemical attack, ordering, and cold work were specially considered. It appears that a kinetic model accounting for time dependence may be envisaged. Some basic recommendations are made for all cases.
A Subnanosecond Risetime Fluxmeter
Authors: Pellinen D. G.
Published: February 2004

A self-integrating search coil with a risetime of approximately 0.4 nsec has been developed for measuring kilogauss magnetic fields in adverse environments. A coaxial calibration fixture with a field risetime of 0.85 nsec was built to calibrate the fluxmeters.
Comments on Lock-In Detection with NMR Saturation in Solids
Authors: Wollan David S.
Published: February 2004

Goldman has shown the perils of lock-in detection for saturated nuclear magnetic resonance (NMR) lines in solids when sweeping through the line in a time τs long compared with the spin-lattice relaxation time T1. We discuss here the case τs«T1, relevant for some solids at high magnetic fields and low temperatures, finding that partial saturation is more easily detected than in Goldman's case. The extension to measurements of dynamic nuclear polarization is also made. Qualitative results for the case τs∼T1 are considered.
An Inexpensive Lock-In Amplifier
Authors: Caplan Lawrence C. , Stern Richard
Published: February 2004

A lock-in amplifier has been constructed, stressing simplicity of design and using inexpensive integrated circuits. At a total component cost not exceeding $200, the unit has a frequency response from 1 Hz to 5 MHz and surpasses the performance of many existing commercial products.
Use of a Multichannel Scaler and Computing Calculator to Generate Optical Transfer Functions
Authors: Klingman E. E.
Published: February 2004

The use of a multichannel scaler as an interface between an edge scan unit and a calculator is described. The system is capable of fully analyzing the scanner data and generating optical transfer functions.
Steam Film Sampling of Water for Mass Spectrometric Analysis of the Deuterium Content
Authors: Thurston W. M.
Published: February 2004

The Leidenfrost effect, characterized by film boiling of a liquid adjacent to a hot metal surface, has been adapted in two forms for sampling water vapor for mass spectrometer analysis to determine the deuterium-to-hydrogen (D/H) ratio. Both a hot probe and a hot plate configuration convert liquid water to vapor without interference from dirt or dissolved material in the liquid phase. Automatic and semiautomatic analysis of the D/H ratio in water has been achieved with a precision of ±0.1 ppm at natural deuterium concentrations. A 2 min cycle time has been used for multiple sampling of bulk water and flowing stream samples.
Instrumentation for the Earth's Field NMR Technique
Authors: Melton B. F. , Pollak V. L.
Published: February 2004

An instrument utilizing free precession in the earth's magnetic field has been developed for studying the field dependence of nuclear spin relaxation in liquids. Both 1H and 19F nuclei are accessible to measurement. The method requires that a current be switched on in the sample coil for a certain time, reduced quickly to some smaller value, and later reduced suddenly to zero. The resulting sample magnetization then precesses about the earth's magnetic field, inducing a voltage in the coil which is amplified and displayed on an oscilloscope screen. The sample coil, current switching circuit, signal detection circuit, and timing circuits are described. The instrument is capable of measuring spin-lattice relaxation times (T1) of 30 msec and up in fields ranging from 2 to 500 G; the range of measurable spin-spin relaxation times (T2) is 10 msec-1 sec in the earth's field of 0.54 G. The signal-to-noise ratio for a 450 ml water sample is greater than 700:1 at a bandwidth of 20 Hz. Estimated precision of the relaxation time measurements is ±3%.
An Autoranging Scale Expander
Authors: Connelly J. A. , Mozersky S. M. , Pessen H.
Published: February 2004

A scale expander for analog signals is described in which the output is presented in the form of an integer voltage (the suppressed voltage) and a voltage representing the remainder of the input signal. Choice of the range (magnitude of suppression) is rapid and automatic. The instrument can be used, as an interface module, with a very wide variety of analog data systems. A few illustrative applications are given. Advantages in instrument performance over presently available circuits are documented.
An Ultralinear 16-Bit Digital-to-Analog Current Converter
Authors: Zander Dennis R.
Published: February 2004

The error analysis and the design of a 16-bit binary digital-to-analog converter are discussed. This method of conversion switches binary weighted constant current sources into a summing junction, in this case the yoke of a CRT. A conversion linearity of 0.00025% and a stability of 0.0004%/h were measured for a full scale current of 1 A showing that a converter linear to better than 16 bits can be constructed requiring no trimming of components.
Comments on Minimum Volume Simple and Compensated Superconducting Coils
Authors: Echarri A. , Sacchetti M. , Spadoni M.
Published: February 2004

The increasing use of superconducting magnets in many fields of research and technology raises more and more often the question: Which is the cheapest magnet for a given field, subject to constraints such as field homogeneity or radial access? In this paper minimum volume coils of three types are analyzed: simple (Fabry), sixth order compensated (outside notch corrected), split (Helmholtz) of internal radii from 1 to 10 cm, and axial apertures (of the Helmholtz coils) from 0.5 to 10 cm. To obtain a given field with a given effective current density Jλ, about the same amount of wire is necessary for a Fabry coil of internal radius 2a1, a sixth order or split coil of internal radii a1, or a split coil with window aperture a1.
Analysis of the Energy Distribution in Cylindrical Electron Spectrometers
Authors: Aksela S.
Published: February 2004

The cases of minimum trace width and second order focus for double focusing cylindrical electron spectrometers are investigated by calculating the energy distributions of transmitted electrons. It is shown that the base width of the electron energy distribution is appreciably smaller in the case of the minimum trace width condition than for the second order focusing arrangement. For high energy resolution, however, the second order focus is found advantageous because the distribution curve has a sharper peak and also a smaller full width at half-maximum for energy spreads (FWHM) less than 0.1%.
A Monophoton Fluorometer with Energy Discrimination
Authors: Schuyler R. , Isenberg I.
Published: February 2004

A recently constructed monophoton time decay fluorometer having several novel features is described. A number of tests of the instrument's performance are presented. A method of moments is used to analyze the data. Single photon energy discrimination permits high collection rates and with coincidence circuitry improves the signal-to-noise ratio. Subnanosecond resolution has been achieved and double exponential decays resolved.
A New Apparatus for Studying Fretting Fatigue
Authors: Hoeppner D. W. , Goss G. L.
Published: February 2004

The problem of fretting fatigue is becoming more acute as increasing demands are placed on materials. Consequently, a program has been initiated to investigate the fundamental mechanisms and conditions that govern fretting fatigue. One of the initial steps taken has been the development of an experimental apparatus and test technique that allows the fretting and fatigue process to occur simultaneously. In addition, loads are monitored continually on the apparatus in the hope that quantitative relationships may eventually be developed relating fretting damage to life. The apparatus is discussed in detail and typical results presented in the paper.
Quadrupole-Octopole Aberration Correctors with Minimum Fields
Authors: Moses Ronald W.
Published: February 2004

Magnetic quadrupole-octopole systems are treated theoretically. A technique is given for finding the minimum octopole field that will correct any geometrical aberration of any orthogonal quadrupole system. It is demonstrated with the correction of aperture aberration and coma in anamorphotic and orthomorphic objective type systems. Further minimization of octopole strengths is achieved by manipulating the quadrupole fields in systems corrected for aperture aberrations. Octopole strengths vary by two orders of magnitude in the cases studied, but chromatic aberrations become large when the octopoles are weakened. Quadrupole-octopole devices that correct the spherical aberration of round lenses are briefly considered. The antisymmetric corrector with minimum fields is very similar to the Archard-Deltrap corrector. It should be at least seven times longer than the focal length of the round lens in order to have fields and chromatic aberrations smaller than those of the best multipole systems without round lenses.
MOS Capacitors for Surface Barrier Electroreflectance Measurements
Authors: Fischer John E.
Published: February 2004

We describe a thin film technique of fabricating samples for surface barrier electroreflectance measurements. Aluminum oxide forms the dielectric spacer and semitransparent nickel is used for the field electrode. The resulting MOS capacitor is transparent from below 0.4 eV to at least 7.5 eV and has no low temperature limitation. Spectra have been obtained on a large class of semiconductor materials using this technique. Qualitative features of the optical response suggest that the surface potential is not clamped by slow surface states, even at room temperature. This method is therefore suitable for quantitative experiments in which the surface field is determined by an auxiliary measurement of surface conductance or capacitance. Application of these preparation techniques to other experiments is suggested.
A Stabilized Metal Vapor Arc Device
Authors: Miyachi Iwao , JayaRam K.
Published: February 2004

This paper presents the description of a wall-stabilized arc device capable of producing the emission lines of metals in a cylindrically stable configuration. An unconventional method of viewing the arc and microphotometer tracings of the photographs of arc discharge as proofs of its symmetry is also discussed. A highly resolved Fabry-Perot recording of the emission line of Cu I at 5153 Å shows the constant emission characteristic of this device.
Fast Switching Pulsed Neutron Polarization Inverter
Authors: Forgacs R. L.
Published: February 2004

A system was developed for producing repetitive short bursts of preferentially oriented spin polarized neutrons for magnetic investigations utilizing neutron spectroscopy. A continuous stream of polarized neutrons from a reactor-monochromator combination is passed through a region in which periodic inversion of polarization is effected by continuous application of an rf field at the Larmor frequency perpendicular to a pulse modulated dc magnetic field. A novel circuit for fast transition modulation of the dc field permits currents as high as 1 A to be switched in less than 2 μsec in the 6 mH dc coil. The maximum burst repetition rate is approximately 83 300 pulses/sec.
An Adsorption Pumped 3He Cooled ir Detector
Authors: Nolt I. G. , Martin T. Z.
Published: February 2004

An ir bolometer is described which demonstrates the use of cryopumping on 3He to achieve temperatures of ∼0.3 K for sensitive detector operation without the usual encumbrances of an external diffusion or mechanical pump. This technique provides a new versatility for 3He cryostats, as demonstrated by the operation of a telescope mounted detector for the past year at Mauna Kea Observatory.
Experimental Apparatus to Investigate Transient Nonlinear Effects in a Plasma
Authors: Marlier S. F. , McIntosh R. E.
Published: February 2004

Laboratory apparatus is discussed in this paper that is useful in measuring the envelope distortion of transmitted high power rf pulses caused by nonlinear plasma processes. The equipment described is inexpensive, easy to fabricate, adaptable, and is well suited for cw as well as transient microwave studies.
Canted Helmholtz Coils for Constant-Gradient Faraday Balance Magnetometry
Authors: Cape J. A. , Young R. A.
Published: February 2004

A canted Helmholtz coils electromagnet for producing a constant gradient magnetic field is described. Used in conjunction with a sensitive balance, the magnet permits accurate magnetrometry, even at low fields, because the field and field gradient are precisely reproducible. We have measured the complete magnetization curve of a thin ferrimagnetic garnet film. The experimental results confirm a theoretical domain model for uniaxial films.
A Determination of Building Materials Dielectric Constant in the Microwave Region
Authors: Hinopoulos B.
Published: February 2004

A method is described for measuring the dielectric constant of building materials mixtures having a relative dielectric constant between 3 and 40 by means of impedance measurements in an open rectangular waveguide terminated by the unknown material. The impedance is determined from the standing wave ratio and a minimum position of the electric field. The method is quite accurate for materials having low to moderate dielectric constants and simpler, especially for mixtures, than other ordinary methods. The difficulties associated with these measurements are due to special problems, such as the suppression of unwanted reflections, and the propagation of a plane wave in a limited space.
A Rapid Scanning Dual Wavelength Spectrophotometer
Authors: Chance Britton , Graham Norman
Published: February 2004

The dual wavelength spectrophotometer, noted for its high sensitivity and accuracy in the recording of oxidation-reduction and other reactions of membrane bound components in turbid suspensions of biological materials, has now been modified to scan the spectrum of these components over a reasonable wavelength range (40 nm) and in a short time (rates as rapid as 20 nm/sec). The baseline precision is not remarkable (approximately 1% error) but the method retains the intrinsic noise rejection properties of the dual wavelength technique. Two forms of the apparatus are discussed, one a simple modification involving a previously described time sharing compensating circuit, and the other incorporating a tapped potentiometer for more precisely correcting the baseline, and a comparator and error detector for correcting wavelength dependent sensitivity error.
A Swept Langmuir Probe at 150 V / μsec
Authors: Friedman William D.
Published: February 2004

A technique is presented for generating a complete Langmuir probe characteristic in 2 μsec with sweep speeds greater than 150 V/μsec. Probe construction with stable lead capacitance is necessary when compensating for the cable displacement current with a current transformer. The probe characteristic is displayed using the X-Y capabilities of a 'scope and results are given for an electron cyclotron resonance heated hydrogen plasma confined in a toroidal quadrupole.
A Mathematical Model of the Arc Pioneer 6/7 Plasma Probe
Authors: Smith Zdenka K. , Day John R.
Published: February 2004

A mathematical model of a quadrispherical electrostatic analyzer is formulated to give the response of such an instrument to a monoenergetic, unidirectional charged particle beam. The model is developed taking into account the aperture and collector geometry and it does not rely on the usual simplifying assumptions that the ratio of the analyzer plate separation to the mean radius is small or that any of the angular or energy acceptance windows are negligible. The model is compared to calibration data and is found to agree well. It is also readily adaptable to the determination of the response function of electrostatic analyzers with other patrial spherical geometries utilizing an arbitrary charged particle distribution input function.
Multipass Laser Interferometry for Plasma Studies
Authors: Heckenberg N. R. , Smith W. I. B.
Published: February 2004

A simple matrix optic theory of multipass laser interferometers shows how a relatively vibration proof system can be easily set up. Measurements made with such systems of the decay of a helium plasma are presented.
A Rapid Inexpensive Method for Determining the Spatial Intensity Distribution of a Laser Beam
Authors: Quinn A. A.
Published: February 2004

A method is described for determining spot size and intensity distribution of a low powered laser by use of inexpensive components normally found in an optics laboratory. The method is useful for routine performance checks of laboratory lasers and as a tool for adjusting focus in optical systems.
A Fringe-Counting Pulsed Ultrasonic Interferometer
Authors: Heydemann Peter L. M.
Published: February 2004

A new ultrasonic interferometer for the automatic measurement of transit times is described. Its main advantage is its ability to follow very large changes of the transit time (1–20) and still maintain a resolution of typically 2.5×10−10 sec. The method is based on the phase sensitive detection of multiple echoes, counting of the output signal at the rate of four counts per full cycle, and an additional interpolation.
Saturation in Continuous Channel Electron Multipliers
Authors: Harris L. A.
Published: February 2004

The steady state gain of electron space current in straight continuous channel electron multipliers is calculated. Ion feedback and space charge effects are neglected, but variation of secondary yield with primary energy and increased wall conductivity due to electron bombardment are considered. Saturation occurs when enough wall current is converted to space current so that the reduced electric field diminishes the effective secondary yield to unity. Predicted results are in good qualitative agreement with reported observations.
A General Purpose Fluid Flow Temperature Controller
Authors: Huber John C.
Published: February 2004

Fluid flow temperature controllers may be used as general purpose laboratory instruments if sufficient flow rate, control flexibility, and ease of design and fabrication are provided. Performance of 220°C/min slew rate and ±0.25°C dead band over the range −180 to 90°C is readily attainable from the instrument with nitrogen gas flows of 60 liters/min when liquid nitrogen is used as heat sink and boiling water as heat source.
X-Ray Detector for Dynamic Diffraction Studies
Authors: Johnson Quintin , Mitchell Arthur , Evans L.
Published: February 2004

A scintillation detector system is described which can be used for dynamic diffraction studies. This system contains several individual channels with each channel (consisting of a scintillator, light pipe, and photomultiplier tube) positioned at a unique 2θ position; thus, measurement of diffracted intensity vs 2θ can be made. Signal-to-background ratio for the (200) reflection of powdered LiF using copper radiation was measured to be 3.0. Angular resolution depends upon the scintillator size and proximity to the x-ray source. For a four-channel system used in x-ray diffraction studies of material undergoing shock wave compression [Q. Johnson, A. Mitchell, R. Keeler, and L. Evans, Phys. Rev. Lett. 25, 1099 (1970)] angular resolution was about 1° in 2θ. This resolution can be increased by methods which increase signal strength.
Analysis of Heat Exchangers for Dilution Refrigerators
Authors: Siegwarth J. D. , Radebaugh Ray
Published: February 2004

Numerical calculations of the behavior of dilution refrigerator heat exchangers are discussed and some results for both discrete and continuous exchangers are presented. It is shown that thermal conductance along the stream is negligible for a typical continuous exchanger of the coaxial tube type, but becomes a dominant feature of a typical discrete exchanger operating below about 50 mK and degrades the performance considerably. A simple design change can be made that reduces the conductance along the liquid and improves the performance of such an exchanger. A simple means of determining whether conductivity is important in either continuous or discrete exchangers is given.
Methods of Measuring the Performance of an Electrostatic Spectrometer
Authors: Roy D. , Carette J.-D.
Published: February 2004

The methods used to measure response and performances of an electrostatic spectrometer with an identical apparatus are studied in the case of the 127° cylindrical spectrometer by means of a method of calculation of the electron energy distribution. The distribution given by the monochromator is calculated and its analysis with the identical analyzer is simulated. The three usual methods of analysis are found to give inaccurate results not only for the widths of the energy distribution but also for its profile. It is shown that because of the inherent angular dispersion of the analyzer, it is necessary to carry out the analysis of the beam by narrow angular slices in order to recover the exact profile of the energy distribution yielded by the monochromator.