bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Nondestructive, Noncontacting Method of Measuring the Depth of Thin Slits and Cracks in Metals
Authors: Hruby Ronald J. , Feinstein Lester
Published: February 2004

A novel method of measuring the depth of ultrathin deep slots in metal surfaces is presented. This method is a noncontacting nondestructive application of microwave theory and practice involving the degeneration of higher cylindrical eigenmodes to the fundamental mode. Theoretical and experimental considerations show a proportionality between the detected signal and the length-depth product. This method complements other procedures for measuring the depth of slots and cracks and provides a new and unique technique for measurement of very thin slots and cracks.
Rapid Charging System for Spark Chamber Pulsers
Authors: Benbrook James R.
Published: February 2004

A solid state switch for use in spark chamber pulsing systems has been developed which permits delaying the recharging of the spark chamber driving capacitor and thus allows high charging current and rapid recycling. This system has been tested in a recent Bevatron experiment at the Lawrence Radiation Laboratory.
Tantalum Hollow Cathode in an Argon Ion Laser Tube
Authors: Carbone R. J. , Witteman W. J.
Published: February 2004

A tantalum hollow cathode used in an argon ion laser as an electron emitter for large currents is described. If the emitter is used in combination with an auxiliary anode, which serves as a starting electrode and as an evaporation shield, we found this cathode a good choice especially for large currents in excess of 100 A.
Frequency Modulation Method for Performing Adiabatic Demagnetization in the Rotating Reference Frame
Authors: Samuelson Gary L. , Ailion David C.
Published: February 2004

A new method for preforming adiabatic demagnetization in the rotating reference frame in NMR experiments is presented in this paper. In this new method the frequency of a crystal oscillator rather than the actual magnetic field is pulsed off resonance. Using simple circuits which are described in this paper, the effective field in the rotating frame can be pulsed by as much as 50 G, depending on the nucleus studied. This method completely avoids the problem of external magnetic field correction due to a pulsed field in the magnetic gap.
A Device for Measuring Crushing Strength of Granular Material
Authors: Linkson P. B.
Published: February 2004

An instrument to record accurately the crushing strength of a single granule has been constructed and tested. The range of crushing strength that can be measured simply depends on the choice of the size of a beam, the deflection of which produces a signal from a differential transformer. It has been demonstrated that extremely low crushing strengths (less than 200 g) can be accurately determined together with the axial deformation of the granule as the load is applied. The loading mechanism allows the crushing force to be applied at a variable and reproducible rate.
The Superconducting Magnetic Flux Detector
Authors: Goodkind J. M. , Stolfa D. L.
Published: February 2004

A superconducting magnetic flux detector which can detect changes in flux as small as 10−11 G·cm2 is now in use in a small number of low temperature laboratories. We describe here how the devices work, how they are made, how they can be used for practical measurements of magnetic susceptibilities or fields, and how they can be made even more sensitive. The devices can easily be used in work other than low temperature physics and should find widespread application.
An Electrostatic Analyzer with No Fringe Field for Measurements of Low Energy Particles on Space Vehicles
Authors: Mariani F.
Published: February 2004

An electrostatic analyzer is discussed which has no fringe field effects. The basic idea is to form the equipotential surfaces around an ideal conductor for which the Dirichlet problem can be exactly solved. It is just the case of any spherical conducting cap, in particular, any hemispherical cap: The equipotential surfaces, in the portion interesting for the trajectory of the particles, are very near to spherical surfaces so that the focusing properties of the ideal hemispherical condenser are still valid. The external surface can act as the container so that another source of perturbation of the electric field is eliminated. The computed and experimental response of the analyzer shows satisfactory agreement for several different geometrical conditions, within the limits due to the expected uncertainties. Some further applications are also mentioned in view of making simultaneous measurements in different energy bands, as well as of determining, in favorable conditions, the potential of the external electrode when it is not zero, which can be the case of an analyzer on board a satellite.
Computer Fitting of Germanium Thermometer Characteristics
Authors: Blakemore J. S. , Winstel J. , Edwards R. V.
Published: February 2004

Of the various kinds of doped germanium investigated for low temperature resistance thermometry, arsenic doping has been found most satisfactory in providing adequate sensitivity over the temperature range from less than 1 to a little over 100 K. Such sensors are highly reproducible as well as sensitive, but for accurate thermometry it has been a disadvantage that the relationship between sensor resistance R and absolute temperature T cannot be expressed accurately in analytic form. However, the relationship can be expressed within close limits over wide temperature ranges by polynomials of the form log10R= ∑ i=0nAj(log10T)i. For an optimum representation, it is necessary to make judicious choices both of the polynomial degree and the temperature range. Insistence on a single polynomial over the entire 1–100 K range produces a solution with spurious oscillations of rms amplitude some 0.3% of the absolute temperature. Such spurious oscillations can be reduced to an amplitude of a few parts in 104 of temperature by using one polynomial for the 1–20 K range and a second polynomial for T≳15 K (thus affording a small overlap region between the two polynomials). The markedly inferior results of using different temperature ranges and a different polynomial regression procedure are illustrated.
Depolarized Light Mixing for Light Beating Spectroscopy
Authors: Wada Akiyoshi , Soda Kunitsugu , Tanaka Toyoichi , Suda Nobuhiro
Published: February 2004

The depolarized light mixing (DLM) system is presented as a useful device in light beating spectroscopy for the observation of molecular rotation, deformation, and reaction which accompany an anisotropic change of polarizability. The system has the following merits: (1) Doppler broadening does not appear because it observes forward scattering; (2) only the line shape coming from a pure anisotropic polarizability change is obtained; (3) it can work automatically as an optical heterodyne system with the stray light from the second polarizer serving as a local oscillator light; (4) there is no difficulty in matching the wavefronts of the scattered light and local oscillator beam; and (5) the scattering volume can be made large without diminishing the efficiency of light beating. These characteristics are described through the numerical evaluation of beating efficiency and signal-to-noise ratio.
A Chemical Reactor Utilizing Successive Multiple Electrical Explosions of Metal Wires
Authors: Johnson Richard L. , Siegel Bernard
Published: February 2004

A severe limitation in the use of the exploding wire phenomenon for chemical synthesis has been the relatively small amount of product that can be prepared by single metal explosions. This problem has been overcome by development of a successive multiple explosion technique in which a large number of wire explosions can be effected in rapid fire order, without breaking the initial vacuum seal. Preset wires are contained in a cylinder which is rotated stepwise over an orifice, thereby dropping the wires into a lower chamber where contact is made with stationary electrodes, across which a high potential has been imposed. This technique is shown to be at least as effective as the single explosion technique in the preparation of compounds that are relatively free of unreacted metal. It was also found that this technique can be used for the preparation of specific particle sizes. The particle size of product powders was found to be quite dependent upon the magnitude of the applied voltage. In general, particle size decreases with increased voltage.
An Automatic Test Set for Measuring the Doping Profile of Semiconductor Epitaxial Layers
Authors: Califano F. P. , Luciano A.
Published: February 2004

The characteristics and the electronic circuit of an automatic test set which can perform the measurement of doping profile of a semiconductor epitaxial layer are reported. The doping profile presentation is on an X-Y plotter. The technique used is that of realizing a Schottky barrier on the epitaxial film and of measuring the capacitance and its derivative vs the reverse voltage applied to the junction. An analog elaboration of this information, according to the Schottky barrier diode equations, finally gives the desired doping profile. Experimental results on different epitaxial layers are reported. If the geometrical dimensions of the Schottky barrier diode are known, an absolute calibration of the carrier concentration is possible.
Image Intensifier Photography of Ultrahigh Energy Cascades in an Ionization Spectrometer. I. Apparatus
Authors: Huggett R. W. , Sandor T. , Webb J. E.
Published: February 2004

Apparatus is described which has been developed to photograph the development of simultaneous nuclear electromagnetic cascades in an ionization spectrometer. Light is emitted by the cascades as they pass through layers of plastic scintillator within the spectrometer. This light is imaged onto the photocathode of a four-stage cascade-type image intensifier with magnetic focusing. When suitable events occur within the spectrometer the intensifier is pulsed so as to transmit and intensify the stored image. The output screen of the intensifier is then photographed. Two optical systems and image intensifier cameras are used so as to obtain right angle stereoscopy of the cascades.
A Three Component Drag Probe for the Measurement of Turbulent Water Velocity Fluctuations
Authors: Earle Marshall D. , Groelle Jack H. , Beardsley George F.
Published: February 2004

Two spherical drag probes which use variable inductance devices as displacement transducers were built to measure turbulent water velocity fluctuations. The associated circuitry provides voltage outputs which are proportional to the three components of force acting on the spherical sensor of each probe. The probes respond to the fluid drag force and also to the fluid inertial force in an accelerating flow field. The frequency at which the response is 3 dB down is 18 Hz for one probe and 41 Hz for the other. The instruments have been calibrated for oscillating flows with velocities from 10 to 150 cm/sec.
A Simple Laser-Triggered Spark Gap with Subnanosecond Risetime
Authors: Alcock A. J. , Richardson M. C. , Leopold K.
Published: February 2004

The construction and operating characteristics of a pressurized laser-triggered spark gap capable of switching voltages exceeding 10 kV with a risetime of less than 300 psec are described. Other desirable features are its low delay and jitter times (∼1 nsec), the ability to deliver rectangular pulses with less than 10% ripple during and after the pulse, and its simplicity of construction. The gap has been investigated using the output of either a single mode ruby laser or a mode-locked neodymium-glass laser as a trigger.
Semiautomatic Hall Effect Measurements System
Authors: Eden R. C. , Zakrzewski W. H.
Published: February 2004

A system simplifying Hall effect measurements is described. With this system the operator effort is reduced from the usual time consuming sequence of control and measurement steps to simply recording the data values. A single digital voltmeter is used to display all the values of currents and voltages required for these measurements and also the temperature of the Hall sample. The proper sequence of measurements, including magnetic field control, is achieved by using a programming switch driven by a stepping motor energized by timers. An original design of a constant current source is included. The output from the digital voltmeter could be connected to a digital punch or automatic data acquisition system providing full automation of measurements.
Collector Turret for Scanning Electron Microscope
Authors: Wells Oliver C. , Bremer Conrad G.
Published: February 2004

A mechanism is described for changing the signal detector in the Cambridge ``Stereoscan'' scanning electron microscope without breaking the vacuum. This has three main advantages. First, it makes it easier to compare the back scattered electron image, the secondary electron image, and the luminescent image, which can help the interpretation in some cases. Second, a spare secondary electron detector can be kept in reserve for high resolution work, thus avoiding the degradation of scintillator performance that occurs after prolonged use. Finally, it makes it possible to optimize detectors by comparing different versions of the same basic design.
Third-Derivative Detection of EPR Signals
Authors: Halpern T. , Phillips W. D.
Published: February 2004

A simple approach for improving the resolution in electron paramagnetic resonance absorption measurements by use of a third derivative technique is presented. The advantages in the case of broad absorption signals as well as of barely resolved lines are discussed.
Photofragment Spectrometer
Authors: Busch George E. , Cornelius John F. , Mahoney Richard T. , Morse Robert I. , Schlosser Donald W. , Wilson Kent R.
Published: February 2004

An apparatus for photofragment spectroscopy, a new type of molecular spectroscopy for dissociative electronic states, is described. Inside an ultrahigh vacuum system, a molecular beam is crossed by pulses of polarized light (from a theta-pinch discharge or from various lasers, including ruby, second harmonic ruby, second harmonic neodymium-glass, and laser pumped tunable dye) and the recoiling photodissociation fragments are detected by a quadrupole mass spectrometer a few centimeters away. The data are collected and analyzed by an on-line time shared computer and presented on a computer driven oscilloscope display as plots of number of fragments detected per microsecond vs time after the laser pulse. Parameters such as photon energy, photon flux, fragment mass, and fragment laboratory recoil angle with respect to the electric vector of the light can be varied to obtain a multidimensional spectrum. This spectrum, the probability of photodissociation as a function of photon energy and flux and of fragment mass, center-of-mass translational energy, and center-of-mass angle of recoil, may be used to study many aspects of molecular states.
Calibration of Piezoelectric Pressure Probe
Authors: Huni J.-P. , Ardila R. , Ahlborn B.
Published: February 2004

Plane Chapman-Jouguet detonations in equimolar acetylene-oxygen mixtures are used to calibrate piezoelectric pressure probes of high spatial and temporal resolution in the range of 1–30 atm. The output voltage of the gauges is found to be proportional to the pressure, V=αP, where α is a calibration constant particular to each probe.
A New Instrument for the Measurement of Liquid Level
Authors: Lindström K. , Kjellander H. , Jonsson C.
Published: February 2004

A new instrument for the measurement of liquid level has been developed, which makes use of the fact that an electric pulse advancing on a transmission line is reflected from any point on the line where the line impedance changes abruptly. Such a change of impedance is obtained at a sudden change of the dielectric constant in the transmission line, i.e., if a fluid is partially introduced in the line. The instrument is further based on the sing-around principle, which gives directly a digital output signal of high accuracy and linearity, in the order of ±0.02%. The instrument can be used for all liquids having a dielectric constant greater than 1.1 or sufficient electrical conductivity.
A Capacitor for Accurate Wide Range Dielectric Constant Measurements on Compressed Fluids
Authors: Younglove B. A. , Straty G. C.
Published: February 2004

A capacitor is described which has been used to make accurate measurements of the dielectric constant of liquid and gaseous oxygen over a wide temperature (55–300 K) and pressure (0.2–34 MN/m2) range. The capacitor is simple to construct and its stability is unaffected by large hydrostatic pressure variations. The temperature variation of the vacuum capacitance is small and remains reproducible even after repeated temperature and pressure cycling.
Generating Cold Gas for Photomultiplier Cooling
Authors: Gerber Jerry
Published: February 2004

The somewhat obvious but relatively unused technique for generating cold gas by bubbling room temperature N2 directly into liquid nitrogen offers twice the cooling time of the conventional immersed heater or continuous gas flowthrough systems. An apparatus for implementing the technique is illustrated.
Technique for Optically Calibrating Streak Cameras
Authors: Davies Terence J.
Published: February 2004

A technique using an optically modulated laser carrier beam has been developed for calibrating the streak speed, linearity, and orthogonality of an image converter streak camera while it simultaneously records experimental data.
The Relative Sensitivities of Polyethylene Shielded Net Radiometers for Short and Long Wave Radiation
Authors: Idso Sherwood B.
Published: February 2004

Many commercially available net radiometers using polyethylene shields to protect their sensing surfaces have 5% of these surfaces covered with a highly reflective white paint. The purpose of this paint is to reduce the sensitivities of these instruments to short wave radiation and make them equal to a supposedly lower long wave radiation sensitivity. Theoretical considerations, however, yield no conclusive evidence for such a differential transmission of short and long wave radiation by thin films of polyethylene. Furthermore, rederivations of the net long wave radiation equations for the calibration chambers of J. P. Funk [J. Sci. Instrum. 36, 267 (1959); J. Geophys. Res. 67, 2753 (1962)] and L. J. Fritschen [J. Appl. Meteor. 2, 165 (1963); 4, 528 (1965)], who pioneered in the construction and evaluation of these instruments, indicate that certain approximations made in the original derivations completely account for the original 5% discrepancy. New experiments verify these findings and demonstrate the equality of short and long wave calibration constants for polyethylene shielded net radiometers without the customary 5% areal covering of white paint.
High Current Density 600 keV Multimomentum Accelerator
Authors: Hilton J. L. , Hamilton G. W.
Published: February 2004

A new type, long focal length, 600 keV, continuous high current density accelerator is described. Beam focus is obtained from a combination of five magnetic and electrostatic lenses. The construction and preliminary multimomentum operation are outlined, wherein a total current of 80 mA at a current density of approximately 40 mA/cm2 was obtained. A simple theory for maximum focused beam current density is developed for semispace charge-neutralized machines which compares favorably with the experimental results. Problems such as back-streaming electrons and required vacuum conditions are discussed. Focus and beam optics are considered for simultaneous acceleration of a multicomponent beam composed of the several molecular ions of normal hydrogen and of a hydrogen-deuterium mixture.
Fringing Field Effect of Deflecting Magnet
Authors: Ezoe Hirohiko
Published: February 2004

The fringing field effect of a deflecting magnet on a charged particle trajectory is examined through its strict analytical expression, and thus the limit of approximation to be applied is discussed. The slope and location of a particle trajectory in the median plane are given, and, for z focusing, the focal length and the location of an assumed thin lens are derived showing how the lens concept can be introduced. The present analysis will give the procedure to obtain the higher order calculations if they are needed.
A Precision Liquid Nitrogen Boil-Off Calorimeter and Its Application to Surface Energy Measurements
Authors: Gilbreath William P. , Wilson Donald E.
Published: February 2004

A liquid nitrogen boil-off calorimeter has been developed and utilized for surface energy measurements. The calorimeter is an all metal, multiwalled chamber which incorporates a means of precisely manostating the calorimetric fluid. The calorimeter also incorporates means for reducing the background pressures in the reaction vessel to 10−8 Torr. This calorimeter was designed to accept heat inputs in the range from 50 to 200 J. An achieved measurement precision of 0.05% in energy permits discrimination of small differences in energy states of the reactions occurring within the calorimeter. The calorimeter has been used to determine the surface energy of a metal film formed by evaporation from a wire.
An X-Ray Macroprobe Analyzer Using Electron Excitation, Design, and Applications
Authors: Toussaint C. J. , Günther K. H. , Vos G.
Published: February 2004

An x-ray macroprobe attachment for the focusing CGR Cristallobloc 31 x-ray spectrometer has been developed. Selected-area analysis in the range 0.01–1 mm2 has been achieved using electron excitation. Focusing devices giving rectangular spot sizes of 1×1 mm and 2×0.15 mm have been used, and devices for sizes 0.2×0.2 mm and 0.1×0.1 mm should be feasible. All elements down to atomic number 5 (boron) can in principle be analyzed by this inexpensive device. Limits of detection of several elements in different matrices are reported. Applications to several metallurgical problems showing the versatility of the macroprobe are reported (examination of a welded joint and detection of silicon and niobium inclusions).
An ac Resistance Bridge and Temperature Controller
Authors: Ries Roger P. , Moore B. Keith
Published: February 2004

A solid state temperature controller is described which is capable of maintaining constant temperature within ±10−6 K at 1 K. The circuit is self-contained and has been used with carbon and germanium resistance thermometers over the range from about 15 to 0.03 K. Bridge balance and heater current are metered, and monitor outputs are included for an oscilloscope display and a strip chart recorder. The bridge circuit is a unique configuration which allows fully guarded cables to the thermometer and higher frequency operation (500 Hz). The control circuit is dual action with separately adjustable integral and linear proportional feedback. Up to 200 mW of control power is available.
Elimination of the Compton Component of Diffusely Scattering Substances
Authors: Ergun S. , Braun W. , Fitzer E.
Published: February 2004

Experimental elimination and determination of the Compton component in diffuse scattering have been made by using crystal monochromated Ag Kα radiation and balanced Rh and Ru filters. The K absorption edge of Ru (λ=0.5605 Å) lies very close to the wavelength of Ag Kα1 (λ=0.5594 Å) so that the intensity obtained using balanced Rh-Ru filters at scattering angles 2θ>20° is essentially the unmodified Ag Kα1 scattering. A procedure is outlined for the elimination of the Compton component at lower angles and for conversion of arbitrary intensities into electron units.
High Resolution Two-Dimensional Interferometry
Authors: Harvey Robin J.
Published: February 2004

A method for increasing the fringe shift resolution of a two-dimensional optical interferogram by more than an order of magnitude without loss of spatial resolution is described. A Fabry-Perot cavity is used as an interferometer to increase the number of passes. The sharpened fringes are multiplied in number by using a multimode laser as a light source. The fringe pattern (observed without a lens) is equivalent to that of a Mach-Zehnder interferometer except that a shift of one fringe corresponds to an optical path length difference of λ/2α (instead of λ) when the cavity lengths are in the ratio L/L0=1/α, and α is the number of excited laser modes.
A Photolysis Lamp for High Intensity, Pulsed Vacuum-Ultraviolet Radiation
Authors: Husain D. , Wiesenfeld J. R.
Published: February 2004

A low pressure z-pinch flash lamp, employing one capacitor and a single spark gap, is described. With an input energy of 2000 J, the pulse width (τe) of the flash was found to be 1–2 μsec, exhibiting continuous emission down to 125 nm with a maximum at 250±10 nm. This simple lamp thus provides a convenient, routine photolytic source of pulsed vacuum uv radiation that may be employed in conjunction with kinetic spectroscopy.
A Phasemeter for Photoelectric Measurement of Magnetic Fields
Authors: Wild P. J.
Published: February 2004

Magnetic fields are sensed by means of the Faraday effect. Corresponding electrical signals in phase quadrature are generated. An auxiliary oscillator is used to obtain a phase modulation proportional to the magnetic field to be measured. Demodulation is performed by a phasemeter described in detail. This phasemeter keeps track of multiples of 2π by digital accumulation and performs linear analog interpolation with an accuracy of 2π/1000. The hybrid digital/analog output has an arbitrarily wide measuring range. In addition, a purely analog output is provided combining the count of increments of 2π with the interpolation. The sampling rate of 40 kHz insures fast measurement response. Results of an experimental magnetic field sensing system incorporating the phasemeter as demodulation unit are presented.
Apparatus for Studying Electron Beam Pumped Semiconductor Lasers and Other High Excitation Density Phenomena
Authors: Nicoll F. H.
Published: February 2004

An apparatus is described for studying high current density bombardment of semiconductors. It operates at voltages up to 30 kV and samples can be cooled to 28 K. The excitation density is high enough to induce lasing in many II-VI and III-V compounds at both 77 K and room temperature. The emission spectrum over a range of current densities is useful in characterizing the doping and impurities in semiconductors.
The Generation of Ultrahigh Hydrostatic Pressures by a Split Sphere Apparatus
Authors: Kawai Naoto , Endo Shoichi
Published: February 2004

A split sphere apparatus has been developed to generate exceedingly high hydrostatic pressures more than 300 kilobars at temperatures over 1500°C in a sample chamber of ample volume. The calibration of pressures is made by the use of known phase transition points in Bi, Fe, and Pb. The calibration above the Pb point (161 kilobars) is discussed in terms of resistance changes for In and CdS previously reported by Drickamer et al.
Conductance Bridge for Electron Tunneling Measurements
Authors: Rogers J. S.
Published: February 2004

An operational amplifier has been combined with a resistance bridge to obtain the properties of a four terminal conductance bridge which is suitable for electron tunneling measurements. The advantages and limitations of the system are described and illustrated.
Time Shared Computers in Some Solid State Physics Research Applications: Data Reduction, Smoothing, and Plotting
Authors: Giovanielli D. , Merrill J. , Luehrmann A.
Published: February 2004

This paper reports several research applications of time shared computers. It has often been claimed that time shared computers cannot be used effectively in research. It is found that, for a large range of experiments in physics, the time shared computer is ideal. Use of a time shared system is less expensive, more interactive, more versatile, and much faster than on-line computer systems. Use of time shared systems is more interactive than batch processing computer facilities. Experimental results are described from a wide range of experiments. The experiments concern plasma waves in solids, color centers in the ultraviolet, and electron tunneling measurements of ir impurity bands in insulators. The results reported demonstrate the wide versatility of the computer experiment system in such areas as data reduction, data smoothing, graphing, and plotting.
Constant False Alarm Rate Bias Control for an Avalanche Photodiode Laser Receiver
Authors: Dobratz B. E. , Farnsworth R. P.
Published: February 2004

A constant false alarm rate closed loop controls avalanche photodiode bias over varying operating conditions such as temperature or ambient illumination and changes in photodiode parameters. The photodiode output is amplified, sensed in a threshold circuit, shaped to a constant amplitude and duration, and integrated. The integrator, also fed by a constant current representing the desired false alarm rate, generates an output proportional to the integrated error in false alarm rate. This control signal alters the photodiode bias until the integrated false alarm rate error is zero.
A 40 keV Pulsed Electron Accelerator
Authors: Quaranta A. Alberigi , Canali C. , Ottaviani G.
Published: February 2004

A pulsed electron accelerator has been built with the following characteristics: energy of the electrons up to 40 keV; average current up to 20 μA; minimum duration of each burst about 70 psec; frequency of repetition of the bursts up to 104 Hz; jitter of the burst with respect to a trigger pulse less than 80 psec; number of electrons per burst (current 5 μA, duration 0.2 nsec) 6.3×103; typical fluctuation on the number of electrons contained in a burst (FWHM) 1%. The accelerator consists of an electron source, made with an electron gun of type commonly used in video tubes, and two pairs of deflection plates perpendicular to each other. The electron beam passes through the plates and the duration of each burst is controlled by a sine wave applied to a pair of plates, while the repetition frequency is controlled by pulses of suitable width and amplitude on the other pair of plates. A pretrigger pulse is available. This accelerator was built to create, in a very short time, a large number of electron-hole pairs (∼8×107 in silicon) within a short distance of the surface of a semiconductor sample. As an application of this technique we describe briefly the measurement of the charge carriers' drift velocity in totally depleted silicon surface barrier junctions under pulsed bias conditions. Other applications are suggested.
High Current Low Voltage Electron Bombarder for Excitation of a Molecular Beam
Authors: Freund Robert S.
Published: February 2004

An electron bombarder for producing intense beams of metastable atoms and molecules has been constructed and operated. The cathode is a 1×5 cm nickel matrix with a BaSrO coating. It has been found to resist poisoning by a variety of gases. The anode consists of 10 parallel channels, each 0.1 cm wide, 5 cm long, and 1 cm high. Anode currents of up to 380 mA at 20 V have been obtained. Beams of N2, helium, and argon have contained approximately 1011 metastables/sec.
NMR Stabilization of a Hall Effect Regulated Electromagnet
Authors: Wing W. H. , Carlson E. R. , Blume R. J.
Published: February 2004

A Hall effect regulated electromagnet system can be locked to an NMR resonance by applying the NMR error signal to a small bias coil on the field sensor. The method requires no modification of the magnet regulator circuitry, produces negligible inhomogeneity near the center of the magnet, and reduces long term field drift to less than 1 mG if the NMR frequency is crystal controlled.
A Combined Differential Thermal Analysis and Spectrophotometric Cell
Authors: Griffiths C. H. , Walker M. S.
Published: February 2004

A high temperature optical cell which allows simultaneous monitoring of thermally induced transformations by differential thermal analysis has been designed and constructed. The α → β phase transformation in both evaporated thin films and bulk phthalocyanine has been studied with the cell and transformation rates determined. The rate constants were approximately three orders of magnitude larger for the bulk sample than for the evaporated films.
A Device for the Production of an Extended Homogeneous Field-Free Spherical Plasma
Authors: de Hoog A. C. , Schott L.
Published: February 2004

A new plasma source has been designed and tested which is capable of producing a stationary, quiescent spherical diffusion plasma of 69 cm diameter. This plasma is free of electric currents, and the electric fields in it can be kept below 10 mV/cm. Electron temperatures between 103 and 3×103 K and plasma densities between 108 and 1010 cm−3 were measured with a Langmuir probe in the pressure range 0.1–10−4 Torr. Radial variations of the plasma density smaller than 10% over about two thirds of the plasma radius were observed in argon at pressures between 10−2 and 10−4 Torr.
A High Current, Subnanosecond Response Faraday Cup
Authors: Pellinen D.
Published: February 2004

A subnanosecond risetime, milliohm resistance Faraday cup was designed and tested for measuring fractional megampere electron beams from pulsed electron accelerators. The device has been typically operated at electron beam currents of 60 kA with an average electron kinetic energy of 4 MeV. Under short circuit conditions the device has measured currents exceeding 0.25 MA.
A High Resolution Mass Spectrometer for Atomic Mass Determinations
Authors: Barber R. C. , Bishop R. L. , Duckworth H. E. , Meredith J. O. , Southon F. C. G. , Van Rookhuyzen P. , Williams P.
Published: February 2004

A high resolution, second-order double-focusing mass spectrometer has been constructed for the precise determination of atomic mass differences. The instrument has a mean radius of curvature in the electrostatic analyzer of 1 m and has operated with a resolving power at the base of the peaks of ∼200 000. Details of current operation are given. The best precision achieved to date is 2.5×10−9, corresponding to ∼250 eV at M = 100 amu; typical precision is ∼5×10−9.
Study of Calibration, Resolution, and Transmission of Electrostatic Velocity Selector
Authors: Leventhal J. J. , North G. R.
Published: February 2004

The calibration, transmission, and resolution of a 127° cylindrical electrostatic velocity selector are examined as functions of the individual voltages applied to the electrodes. The calibration and resolution calculated using first order orbit theory are compared with numerically determined orbits obtained using the exact electrostatic field within the selector. The calibration and transmission are found to be strongly dependent on the electrode potentials while the resolution is insensitive to these parameters. The experimentally determined resolution is in good agreement with the calculations. Variation of the transmission with the individually applied voltage is shown to be the result of vertical focusing.
Spectrometer Shield for Stray Iron X-Ray Radiation in the Scanning Electron Microscope
Authors: Ballard D. B. , Yakowitz H. , Siems S.
Published: February 2004

A spectrometer shield for stray iron x-ray radiation was devised and installed in the scanning electron microscope. A modification to the touch alarm was also made to make the system operative.
Coaxial Slotted Line Modified for Dielectric Measurements on Hygroscopic Materials
Authors: Nanassy A. J.
Published: February 2004

A modification of coaxial slotted line, General Radio type 874-LBB, for dielectric measurements on hygroscopic materials at temperatures from −50 to 100°C is described. Provision is made for dielectric measurement at various relative humidities in a cell enclosing the modified line.
Stationary Platinum Electrode for Measurement of O2 Exchange by Biological Systems under Hydrostatic Pressure
Authors: Chandler M. Trevor , Vidaver William
Published: February 2004

An electrode assembly has been constructed for the purpose of measuring polarographically rates of photosynthetic or respiratory oxygen exchange of biological systems while exposed to hydrostatic pressures of up to 1400 atm. The apparatus may also be used to measure changes in dissolved oxygen concentration brought about by metabolic activity while under pressure. Some typical results are presented.
A Practical Nuclear Quadrupole Resonance Thermometer
Authors: Labrie R. , Infantes M. , Vanier J.
Published: February 2004

The paper describes a system forming a precise nuclear quadrupole resonance (NQR) thermometer based on the resonance line of 35Cl in KClO3. The system includes a transistorized Robinson oscillator for the detection of the NQR absorption signals. Details of the oscillator design are given and the method of detection of the NQR absorption signals through frequency modulation is described. The oscillator is locked to the NQR absorption line through a feedback loop including a phase sensitive detector. Conversion of frequency modulation to amplitude modulation in the amplifier section is partially avoided through the use of a second feedback loop which locks the amplifier tuning frequency to the oscillator frequency. An accuracy of the order of 0.003°C in temperature determination at liquid nitrogen temperature is obtained.
Evaluation of an LN2-Temperature Solid State Spectrometer for Rocket Borne Experiments
Authors: MacGregor G. A. , Turiel I. , Bettenhausen R. , Iantuono A.
Published: February 2004

A rocket borne solid state spectrometer was used recently during a solar flare to detect solar x-ray emissions in the energy range 4–40 keV. The silicon detector, cooled by liquid nitrogen and incorporating an optical feedback preamplifier, is believed to be the first such detector used in this type of experiment. This paper evaluates the spectrometer and detection system under laboratory and field conditions, offering calibration data and some experimental results. Suggestions are made for future experimentation.
Supercollimation of Negative Ion Beams with Apertures
Authors: Armstrong D. D. , Wegner H. E.
Published: February 2004

A technique for producing highly collimated beams of negative ions using apertures is discussed. The application of the method produced a 30 μ diam H− beam with an angular divergence of 1.5 mdeg. The results of a study of the small angle scattering of protons from a carbon are presented. Other possible applications are outlined.
Tandem Mass Spectrometer for Secondary Ion Studies
Authors: Benninghoven A. , Loebach E.
Published: February 2004

An instrument permitting the study of ionization processes caused by ion and electron impact on solid surfaces under well defined conditions is described. It consists functionally of a single focusing mass spectrometer providing a monoisotopic and monoenergetic primary beam and a quadrupole mass spectrometer for the analysis of secondary ions released from a target surface. Low primary ion current densities and ultrahigh vacuum conditions allow investigations without essential alterations of the target surface during experiment. Some results demonstrating instrument performance are presented.
Optical Film Thickness Monitoring
Authors: Bey Paul P.
Published: February 2004

Experiments and theoretical calculations are carried out to determine the accuracy attainable by intensity modulation and wavelength modulation optical monitoring techniques used to specify film thickness. Experimental results show that film thickness errors of 5% are typical in deposition thickness monitoring based on intensity modulation techniques. It is demonstrated by calculation that an appreciable improvement of film thickness accuracy can be obtained by wavelength modulation techniques, and that variable wavelength dielectric filters may conveniently be used as spectral filters for wavelength modulation devices to provide a film thickness accuracy between 0.5 and 1%. Results obtained may be used for the design of optical thickness monitoring systems.
Gain Fatigue Mechanism in Channel Electron Multipliers
Authors: Prince R. H. , Cross J. A.
Published: February 2004

A study of the instability in surface composition of reduced lead oxide glass surfaces is described which suggests a possible mechanism for the observed gain degradation of channel electron multipliers in high vacuum environments. In particular, the depletion of surface oxygen from initial levels which were up to 10 times the stoichiometric concentration was observed, using the method of Auger electron spectroscopy. A model incorporating surface oxygen as a possible donor species in the secondary emission process is discussed, which qualitatively predicts the observed pressure dependence of multiplier gain and the onset of fatigue at about 10−7 Torr.
Helium Temperature EPR System with Iris Tuning and Sample Interchange Capabilities
Authors: Schacher Gordon E.
Published: February 2004

An EPR system for use at liquid helium temperatures is described. The design of this system is such that one can interchange samples and adjust the cavity coupling when operating at liquid helium temperatures. Samples can be interchanged when operating below the lambda point without disturbing the helium bath. Also, the system includes a goniometer for angular dependence studies.
Frequency Control for Time Averaging in Frequency Swept Magnetic Resonance Spectroscopy
Authors: Brooker H. R. , Startup W. W.
Published: February 2004

A system is presented for controlling the frequency sweep of a cw self-oscillating magnetic resonance spectrometer. The system incorporates a Hewlett-Packard synchronizer, model 8708A, which covers a total range of 50 kHz–430 MHz. The frequency control is sufficiently precise that, when the linewidth to frequency ratio is 10−5 or more, averaging may extend over several hours. Details are given for applying the system to quadrupole resonance of chlorine.
Efficiency of Channel Electron Multipliers for Electrons of 1–50 keV
Authors: Archuleta R. J. , DeForest S. E.
Published: February 2004

The calibration of the University of California, San Diego (UCSD) plasma detector on board Applications Technology Satellite 5 (ATS-5) has been used to determine the shape of the efficiency vs energy curve for channel electron multipliers. Results are compared with other workers with reasonable agreement. The measured efficiencies are well expressed in the range 1–50 keV by ε=1−{2/[3+6.5/(E−0.5)+30/(E−0.5)3]}.
Optical System for Direct Spatially Resolved Measurements of Radiative Emission and Self-Absorption of Extended Bodies
Authors: Rogoff Gerald L.
Published: February 2004

A simple optical system has been designed for making spatially resolved measurements of the emission and self-absorption of an extended radiator. The system, which is a highly efficient collector of radiation, isolates a conical region extending through the radiating body. If the radiator is uniform along the line of sight, no mathematical inversion is required to determine the local emission and absorption coefficients. Since the isolated region is the radiation source for measuring its own absorption, source and absorber are identical, and the analysis for wavelength dependent absorption is simplified. The system can also be used for making spatially resolved measurements of the absorption of externally generated radiation. This paper describes the basic concept as well as an instrument containing only reflection optics that has been constructed for measuring radial profiles of radiative properties of a gas discharge plasma.
Electron Bombardment Ionizer for Accelerated Molecular Beams
Authors: Parks E. K. , Young C. E. , Wexler S.
Published: February 2004

An electron bombardment ionizer for accelerated molecular beams is described which utilizes the electron space charge potential well to suppress ions formed from molecules with thermal energies. Ions produced from molecular beams that have been aerodynamically accelerated in seeded supersonic jets to kinetic energies above 2 eV have been separated from ions formed from the propellant light molecules and background gas. The efficiency of the ionizer is approximately a factor of 10 lower than that of conventional high efficiency electron bombardment ionizers.
Shielding of Low Magnetic Fields with Multiple Cylindrical Shells
Authors: Freake S. M. , Thorp T. L.
Published: February 2004

The factors which determine the minimum magnetic field inside a set of cylindrical shields of high permeability material are summarized. Using this information a three cylinder system was designed and constructed to screen out the earth's magnetic field inside the Dewar of a dilution refrigerator to less than 5×10−5 Oe.
New Techniques for Differential Pumping Systems
Authors: Schmidtke G.
Published: February 2004

Differential pumping may be made more efficient by application of modified collimators of the grid type, first used for optical collimation only in spectrometers for the extreme uv spectral region. Compared with conventional types of differential pumping, either larger windows can be used, or the gas flow can be reduced. For optical purposes we had to build up a system with a rather large window, with an effective area of 15 mm2. The differential pumping properties of this system are compared to those of a conventional pumping system with an effective area of 3 mm2 and the results clearly show the advantage of the new design.
Atmospheric Pressure Pulsed CO2 Laser with Brass Electrodes
Authors: Merchant V. , Irwin J. C.
Published: February 2004

The characteristics of a transversely excited atmospheric pressure (TEA) CO2 laser with a new electrode arrangement have been investigated. The electrode arrangement consists of two brass bars as anode and cathode with two flat side electrodes held at the same potential as the anode. The laser output is compared to that obtained from a conventional TEA laser in which the cathode consists of a row of resistors.
An Improved Method for Measuring Photoemission Electron Energy Distribution Curves
Authors: Palmer Richard E.
Published: February 2004

In many photoemission experiments the retarding voltage between the emitter and the collector is modulated to obtain an electron energy distribution curve. A technique is described in which the incident light beam is modulated as well, but at a much higher frequency. Problems arising from electronic and lamp noise and from stray shunt capacitance are reduced. If the light is modulated by varying its polarization, as in an experiment to study ``surface'' photoemission, the effects of reverse photoemission can also be reduced.
Directional Sensitivity of Hot Film Sensors in Liquid Metals
Authors: Hill James C. , Sleicher Charles A.
Published: February 2004

In order to determine whether the thick thermal boundary layers in liquid metals lead to reduced directional sensitivity of hot film sensors, steady state calibrations for speed and directional sensitivity of cylindrical hot film sensors having aspect ratios of about 19 were made in a liquid metal by towing them through a long pool of mercury. The directional sensitivity is characterized by an empirical parameter, k, which varies from zero to one as the sensitivity varies from its maximum to zero. The results show that for measurements of flow direction, the sensor aspect ratio must exceed 20 for sensor Peclet numbers less than about 0.35. The k are only weakly dependent on angle of inclination in the range 30–60°, a result which can be used to reduce the labor of calibration.
A Technique for Efficiently Converting 13CH4 into Pyrolytic 13C
Authors: Goosman D. R.
Published: February 2004

A method is described for producing pyrolytic carbon with efficiencies suitable for use with highly enriched isotopes. Dense cylinders 14 cm long×1.4 cm in diameter have been produced with 97% efficiency by the pyrolysis of 13CH4. A process for converting 13CO into 13CH4 is also described briefly. Some applications for nuclear spectroscopy are discussed.
A New Laboratory Gas Circulation Pump for Intermediate Pressures
Authors: Reilly J. J. , Holtz A. , Wiswall R. H.
Published: February 2004

A laboratory gas circulation pump has been built in which the pump driving force is obtained by the alternate decomposition and regeneration of vanadium dihydride (VH2). This cyclic action is accomplished by alternately heating and cooling the hydride system using hot (50°C) and cold (18°C) water. The particular pump described is suitable for the circulation of gases in systems where the pressure range is between 7 and 24 atm.