Showing papers in "Review of Scientific Instruments in 1967"
TL;DR: In this article, a study has been made of all the known factors which limit the performance of high resolution (0.07 to 0.01 eV FWHM) monochromators.
Abstract: A study has been made of all the known factors which limit the performance of high resolution (0.07 to 0.01 eV FWHM) monochromators. These limiting factors have been incorporated into design equations for the optimum (maximum current output) monochromator. The conclusions are tested by performance measurements on a prototype instrument. The results require the introduction into the design equation of a new limiting factor, an anomalous energy spread in dense electron beams, which is empirically determined.
332 citations
TL;DR: In this paper, a diamond anvil driven by a simple piston and screw device has been used to subject solid samples to pressures up to 300 kbar at ambient room temperature at room temperature.
Abstract: Diamond anvils driven by a simple piston and screw device have been used to subject solid samples to pressures up to 300 kbar at ambient room temperature. Samples can be examined optically and by x‐ray diffraction while under pressure. Pressure is measured by means of the lattice parameter of sodium chloride mixed with the sample. Reflectivity and volume data on iron, as well as crystallographic data on PbS, PbSe, and PbTe, are presented.
209 citations
TL;DR: In this article, a cylindrical capacitor was used as an analyzer for charged particles in the relativistic region, and the results of the analyzer were shown to be unrestricted.
Abstract: The study of the dynamic and optical properties of the cylindrical capacitor as an analyzer for charged particles is extended to the relativistic region. The proposed analyzer is found to be absolutely unrestricted by the relativistic effect, the latter introducing some changes which do not however impair the analytical features of the device. The emission angle for which there is a second order focus is energy‐dependent, shifting from θ0=42°18.5′ in the nonrelativistic case to θ0=55° in the ultrarelativistic case. It is shown that the usual derivation of the relativistic formulae from the nonrelativistic ones by replacing the nonrelativistic potential difference by an ``effective relativistic potential difference'' is incorrect for electrostatic devices, unless this quantity is given a specifically ``electrostatic'' form, distinct from the magnetic one. The figures of merit of the analyzer concerning resolution and luminosity are comparable with those of the best magnetic spectrometers. The analyzer seems to be simpler and cheaper than the magnetic type, but calls for very high deflecting voltages, which may be a disadvantage in operation.
190 citations
TL;DR: In this article, the authors used 3 platinum-encapsulated 4-lead germanium resistance thermometers for use in precision calorimetry from 1 to 25°K.
Abstract: The cryogenic apparatus and techniques used to calibrate 3 platinum‐encapsulated 4‐lead germanium resistance thermometers for use in precision calorimetry from 1 to 25°K are described. The calibration data for each thermometer were fitted with the aid of a digital computer by a polynomial expressing logR in terms of powers of logT. The sensitivity and temperature‐cycling stability of these thermometers were adequate to recommend this type of temperature sensor for accurate low temperature calorimetry. A test of the temperature scale and of an isothermal type calorimeter was made by measuring the heat capacity of a sample of 99.99+% copper from the 1965 Calorimetry Conference Copper Standard and comparing the results with those obtained by other investigators. An equation to represent the heat capacity of pure copper from 1 to 25°K, based upon appropriate literature results and the present data, is offered as a convenient copper reference equation for intercomparison of heat capacity results from various laboratories.
166 citations
TL;DR: In this article, the behavior of standing wave accelerator tanks, made up of chains of resonant cavities, is investigated using a coupled resonator model, which gives accurate predictions of the behaviour of such a cavity chain, including tolerances to errors in manufacture, cavity feed distributions, and transient response.
Abstract: The behavior of standing wave accelerator tanks, made up of chains of resonant cavities, is investigated using a coupled resonator model. This model gives accurate predictions of the behavior of such a cavity chain, including tolerances to errors in manufacture, cavity feed distributions, and transient response. The parameters necessary in the theory, the cavity couplings, Q's, and frequencies, may easily be determined by experiment. Extension of the simple chain to a more complex chain with double periodicity and second nearest neighbor coupling is demonstrated. Advantages of operating such accelerators in the π/2 mode are shown.
132 citations
TL;DR: In this article, the electron multiplier detection efficiency for positive ions determined as a function of incoming ion energy, velocity and degree of ionization was analyzed and compared to positive ion detection efficiency.
Abstract: Electron multiplier detection efficiency for positive ions determined as function of incoming ion energy, velocity and degree of ionization
109 citations
TL;DR: In this article, a technique has been developed to generate hydrostatic and uniaxial stress regimes, using a Teflon cell as a container in a conventional pistoncylinder device.
Abstract: A technique has been evolved to generate hydrostatic and uniaxial stress regimes, using a Teflon cell as a container in a conventional piston‐cylinder device. Details of the technique and calibration procedure are described. The possibility of using high resistivity as‐grown n‐GaAs for pressure measurement is indicated. Piezoresistive effects in oriented n‐Si plates were used to determine the nature of stress distribution in the pressure medium. The usefulness of the technique to semiconductor studies is pointed out.
107 citations
104 citations
TL;DR: In this article, a magnetometer was developed which utilizes a superconducting quantum interference device (SQUID) as a sensor, and permits digital and analog measurements of magnetic fields.
Abstract: A magnetometer was developed which utilizes a superconducting quantum interference device (SQUID) as a sensor, and permits digital and analog measurements of magnetic fields. The digital mode permits measurement of large field changes with a constant accuracy of approximately 1/10 the natural periodicity of a SQUID. (The natural period is typically 10−6–10−3 G.) Thus, the precision of measurement of large field changes is high. The analog mode is advantageous for high precision measurement, of the order of 10−8 G, but for small field changes. Combined mode measurements permit the very high precision of the analog mode to be combined with the large range of the digital mode. The digital mode, which represents an improvement over the original lock‐on magnetometer, utilizes two synchronous detectors to provide signals which uniquely determine the instantaneous magnetic bias of the SQUID. The synchronous detector outputs drive a novel logic circuit which produces appropriate add‐subtract pulses to a digital c...
98 citations
TL;DR: In this paper, a technique for producing monodisperse sprays is described, which makes use of Rayleigh's criterion for the breakup of capillary jets by mechanically vibrating a number of uniform size capillary needles arranged in parallel.
Abstract: A technique for producing monodisperse sprays is described. The technique makes use of Rayleigh's criterion for the breakup of capillary jets by mechanically vibrating a number of uniform size capillary needles arranged in parallel. It was used to produce sprays in the size range of 290–950 μ, but in principle there is no reason why this range cannot be extended. The regime of spray sizes where drop coalescence is likely to take place is delineated, and methods of minimizing coalescence are described.
96 citations
TL;DR: In this paper, a feedback control theory for constant-temperature hot-wire anemometers is developed in the form of a linear differential equation of the third order, which allows a more detailed and clearer description of the anemometer's behavior than can be obtained by the frequency response method.
Abstract: A feedback control theory for constant‐temperature hot‐wire anemometers is developed in the form of a linear differential equation of the third order This theory allows a more detailed and clearer description of the anemometer's behavior than can be obtained by the frequency response method which has been applied until now to constant‐temperature hot‐wire anemometers The theory is presented for the case of an equal arm bridge in the feedback system Although the theory is restricted to small velocity fluctuations, it is assumed that large fluctuations may be measured correctly within approximately the same frequency range as small ones The theory is applied to the optimization of the frequency response of constant‐temperature hot‐wire anemometers by means of a square wave test
TL;DR: In this article, a low inductance three-electrode spark source for the vacuum ultraviolet fed by a 20kV, 13μF capacitor is described, whose main feature is its ability to generate spectra of very high degrees of ionization.
Abstract: A low inductance three‐electrode spark source for the vacuum ultraviolet fed by a 20‐kV, 13‐μF capacitor is described. Its main feature is its ability to generate spectra of very high degrees of ionization. A 6‐kV spark produces spectra of CV and CVI as well as FeXVI, while a 17–18‐kV spark yields FeXVIII, AlXII, and AlXIII.
TL;DR: In this paper, the transmission characteristics of spherical plate electrostatic analyzers for external sources are determined analytically and graphically using derived relationships between these parameters and the position of the center of the particle's trajectory, which trajectory is approximated by a circular arc.
Abstract: The transmission characteristics of spherical plate electrostatic analyzers for external sources are studied. Transmission as a function of particle point of incidence, angle of incidence, and kinetic energy, and of analyzer plate geometry (central angle and radii of curvature) and plate potentials, is determined analytically and graphically. Our method (which assumes that the ratio of plate spacing to mean radius is small) uses derived relationships between these parameters and the position of the center of the particle's trajectory, which trajectory is approximated by a circular arc. For a fine incident beam of particles, angular resolution at mean transmitted energy and energy resolution at normal incidence are independent of the point of incidence; the angular resolution is moreover a constant and the energy resolution varies linearly with the mean energy. The area of energy‐angle transmission diagrams is likewise independent of point of incidence. Energy and angle response functions for diffuse beams of particles are derived semi‐empirically. The energy response function (integrated over angle) has the same FWHM as the function for a fine beam incident normally. The angle response function (integrated over energy) has the same FWHM as the function for a fine beam at appropriate fixed energy. Theoretical results for fine beams are compared with experiment and agree well. A practical instrument, specifically for satellite use but suitable for the laboratory, is also described.
TL;DR: In this article, an apparatus for the differential thermal analysis of small (1.7 ml) samples of solutions is described, and a heat effect amounting to 50 cal per liter of solution taking place over a 30° temperature interval can be measured with a precision of 5%.
Abstract: An apparatus for the differential thermal analysis of small (1.7 ml) samples of solutions is described. A heat effect amounting to 50 cal per liter of solution taking place over a 30° temperature interval can be measured with a precision of 5%, and a change in heat capacity of the solution amounting to 2 cal deg−1 per liter of solution can be measured with a precision of 15%.
TL;DR: In this paper, a new technique was described for constructing vapor cooled leads used to introduce electrical currents into liquid helium, which can be constructed to carry optimum currents ranging from low values (less than 100 A) to very high values (several thousand amperes).
Abstract: A new technique is described for constructing vapor cooled leads used to introduce electrical currents into liquid helium. Using this method, leads can be constructed to carry optimum currents ranging from low values (less than 100 A) to very high values (several thousand amperes). The current carrying elements are small (No. 38) silver‐plated copper wires woven into the shape of cylindrical tubes (i.e., electrostatic shielding). This fine division of the current carrying elements allows very good heat exchange with the helium boil‐off gas. Helium losses are approximately 2.71×10−3 liter/h A for a pair of leads operating at the optimum current.
TL;DR: A two stage electrostatic aerosol sampler capable of accurate sampling of micron and submicron size aerosols onto any flat collecting surface of an area up to 5×10 cm2 is described and has been found to be very satisfactory for obtaining aerosol samples for electron or light microscopy.
Abstract: A two stage electrostatic aerosol sampler capable of accurate sampling of micron and submicron size aerosols onto any flat collecting surface of an area up to 5×10 cm2 is described. Size classification of the deposited aerosol is prevented by the use of a novel pulsed precipitating electric field. Sampling efficiency and the uniformity of the deposited aerosol has been determined using monodispersed flourescent aerosols over the size range from 0.028 to 3.2 μ. The sampler has been found to be very satisfactory for obtaining aerosol samples for electron or light microscopy.
TL;DR: In this article, a simple, versatile, magnetic float densimeter that can be used to measure the density of liquids as a function of temperature has been described and calibrated with water from 20 to 50°C demonstrating a sensitivity of 0.3 ppm and precision of 2 ppm.
Abstract: A simple, versatile, magnetic float densimeter that can be used to measure the density of liquids as a function of temperature is described. The system has been calibrated with water from 20 to 50°C demonstrating a sensitivity of 0.3 ppm and a precision of 2 ppm. The accuracy of the densimeter has been verified by measuring the densities of NaCl solutions at 25°C. Excellent agreement with previously published data was achieved.
TL;DR: In this article, a superconducting circuit has been used in a sensitive magnetic susceptibility apparatus to detect changes in magnetic susceptibility as small as 10−10 cgs/g in a 104 Oe field, and in a low field magnetometer with which magnetic fields as low as 5×10−7 Oe have been measured.
Abstract: A new superconducting circuit has been used in a sensitive magnetic susceptibility apparatus to detect changes in magnetic susceptibility as small as 10−10 cgs/g in a 104 Oe field, and in a low field magnetometer with which magnetic fields as low as 5×10−7 Oe have been measured. A low field superconducting shield for testing sensitive magnetometers has been developed and used to provide stable magnetic fields of less than 10−6 Oe, maintained stably for as long as six days. The measured attenuation of externally applied axial field changes is shown to be a factor of about 31 per shield radius. The stability of the persistent field of a Nb‐25% Zr superconducting solenoid, observed over an 8 h period, indicated an average drift in the persistent solenoid field of less than one part in 1010/sec. Also, the attenuation of various high field magnetic shields of Nb‐25% Zr foil was measured.
TL;DR: In this paper, an apparatus for measuring the Hall effect of low mobility samples at high temperatures is described, where an alternating current at 510 cps, in conjunction with a low frequency magnetic field at about 2 cps is used.
Abstract: An apparatus is described for measuring the Hall effect of low mobility samples at high temperatures. The measuring method is of the double ac type. An alternating current at 510 cps, in conjunction with a low frequency magnetic field at about 2 cps, is used. The use of single or double phase sensitive detection is discussed. A temperature controller with a stability of about 2×10−2 C° at 1000°C and a sample holder assembly are described. Results of measurements on NiO samples are given, indicating a noise level equivalent to mobilities of 3×10−4 cm2/V sec.
TL;DR: In this article, the authors present the status of a program directed toward the improvement of ion sources and the technology of intense dc ion beams, which are especially suited to proton production and to molecular ion production at source arc currents of up to 50 A.
Abstract: The present status of a program directed toward the improvement of ion sources and the technology of intense dc ion beams is described. The work is in the energy range of from 20–600 keV at currents of up to 1 A. Several factors have differentiated the approach from that existing in some other areas of ion beam research. There are severe cooling problems in the ion source and in beam targets. Grids cannot be used in the electrode system, and many of the techniques which have been used to study detailed emittance shapes are very difficult to utilize because of these thermal problems. On the other hand, it is possible to accumulate electrons in these dc beams to eliminate the dispersive effect of space charge. Pulsed beams with on‐times of less than a few hundred microseconds ordinarily are completely unneutralized. Ion sources are described which are especially suited to proton production and to molecular ion production at source arc currents of up to 50 A. Single gap accelerating and focusing arrangements are described. A special configuration prevents electron trapping and subsequent break‐down in the combined electric and magnetic fields.
TL;DR: In this paper, the effect of baseline restoration on signal-to-noise ratio in pulse-amplitude measurements is determined theoretically and experimentally, and the results are presented for the three commonly used filters: CR-RC filter, quasi-Gaussian filter, and delay-line filter.
Abstract: The effect of baseline restoration on signal‐to‐noise ratio in pulse‐amplitude measurements is determined theoretically and experimentally. It is found that the signal‐to‐noise ratio with baseline restoration normalized to that without restoration is ηr/η=[1+α− 2α½kx(τ)]−½, where kx(τ) is the noise correlation factor at the output of the filter (amplifier), τ is the measurement interval, and α is the attenuation of noise power due to integration by the restorer capacitance and switch resistance (α=1 for fast restorer). Methods of calculation of correlation functions are outlined. A method for measurement of correlation functions by oscilloscope is described. The results are presented for the three commonly used filters: CR‐RC filter, quasi‐Gaussian filter, and delay‐line filter. Baseline restoration is found to degrade the signal‐to‐noise ratio. The amount of this degradation can be reduced to negligible proportions in filters with long memory (such as CR‐RC) by a small degree of integration in the restor...
TL;DR: In this paper, a wide band, variable frequency nuclear magnetic resonance spectrometer is described for use with either a crossed-coil induction probe in the frequency range 2 to 40 MHz or a parallel T rf bridge from 2 to 90 MHz.
Abstract: A wide band, variable frequency nuclear magnetic resonance spectrometer is described for use with either a crossed‐coil induction probe in the frequency range 2 to 40 MHz or a parallel T rf bridge from 2 to 90 MHz. A novel use of simple rf circuits is described wherein the receiver amplifier has useful gain to 95 MHz and the transmitter amplifier has useful gain to 45 MHz. A simple modification of the Varian Associates 8 to 16 MHz induction probe for use with this circuit to 40 MHz is described. Sensitivity of the instrument with both the probe and bridge compares most favorably with a commercial induction spectrometer. The circuit is essentially free of microphonic noise.
TL;DR: In this paper, the thermoelectric output of high-fired thoria-insulated thermocouples was determined and found to be reliable up to at least 2850°C, when corrected for electrical shunting through the insulation.
Abstract: Tungsten‐rhenium thermocouple systems were evaluated for use in measuring temperatures between 1600 and 3000°C. Temperature‐millivolt relationships were extended from 2300 to 3000°C for bare‐wire W3Re/W25Re and W5Re/W26Re thermocouples in vacuum. The performance of W26Re sheathed, high‐fired beryllia‐insulated thermocouples was limited only by the melting point of the beryllia insulation (∼2550°C). The thermoelectric output of high‐fired thoria‐insulated thermocouples sheathed in W26Re was determined and found to be reliable up to at least 2850°C, when corrected for electrical shunting through the insulation. Stability of high temperature thermocouples using thoria insulation was within ±0.3 mV (±40°C) when held at 2425°C for 148 h.
TL;DR: In this paper, a technique for measuring the thickness of silicon films grown epitaxially on sapphire is described, which is performed in situ and can be used to monitor film thickness while the film is growing.
Abstract: A technique for measuring the thickness of silicon films grown epitaxially on sapphire is described. The method is nondestructive, is performed in situ, and can be used to monitor film thickness while the film is growing. The method utilizes the infrared emission from the sapphire substrate and from the growing film. The radiation from the sapphire substrate is partially transmitted through the silicon and partially reflected in the silicon, establishing an interference pattern which can be used to determine silicon film thickness. Using a detector with peak sensitivity at 2.4 μ, silicon film thicknesses to the nearest ±0.1 μ are readily measurable. The absolute accuracy of ±0.1 μ is independent of film thicknesses. Films in the range from 0.1 to 15 μ have been measured. Increased detector sensitivity can extend the maximum measurable film thickness.
TL;DR: A Langmuir probe system has been developed for measurement of electron densities and electron temperatures in the lower ionosphere as discussed by the authors, which can be used to determine both the electron density and electron temperature simultaneously and continuously.
Abstract: A Langmuir probe system has been developed for measurement of electron densities and electron temperatures in the lower ionosphere. While the probe works like the Smith probe, it has various practical advantages. It is an all electron system working on a single floating power supply. This makes the actual system simpler and allows for more thorough prelaunch checkouts while the rocket is on the launch pad. Further, this system can feed an additional guard electrode without the use of any additional electronics. It has greatly helped in reducing the current leakage and the effect of the distributed capacity at the input of the amplifier. Also the sweep used is such that capacitive discharge currents between the sensor and the rest of the system do not appear in that part of the sweep where retarding potential analysis is done for determination of electron temperature. Within this system it is possible to control the sensor voltage with the output of the amplifier and keep it at space potential. In principle this method can be used to determine both the electron density and electron temperature simultaneously and continuously.
TL;DR: In this article, the authors describe the instrumentation and in-flight performance of the rubidium vapor magnetometers being flown by the National Aeronautics and Space Administration on the POGO satellites.
Abstract: This paper describes the instrumentation and in‐flight performance of the rubidium vapor magnetometers being flown by the National Aeronautics and Space Administration on the POGO satellites. An optically pumped, self‐oscillating rubidium magnetometer was selected as being most compatible with the objectives of the study and with the spacecraft capabilities. A four absorption cell configuration is used to reduce the effect of the null zones inherent in these instruments and to obtain accuracies compatible with the scientific objectives of the program. Scalar magnetic field data are obtained in both digital (PCM) and analog (frequency multiplex) form. Instrument performance parameters are monitored through both main frame and subcommutated PCM data. The first instrument orbited was aboard OGO‐II which was launched on 14 October 1965. This instrument has returned a large quantity of data, and is still operating when sufficient spacecraft power is available. The accuracy of the data is determined, apart from orbit accuracy, by spurious phase shifts within the instrument. These arise from such sources as optical axis misalignment, electronic nonlinearities and frequency dependence, and propagation delay over the long cables connecting sensor and electronics. The magnitude of the resulting error is inversely proportional to the phase slope of the dual cell absorption line. The total effect in the POGO instrument of these sources of error is an accuracy of better than 1.5γ over the entire instrument range of 15 000 to 64 000γ.
TL;DR: In this paper, it was shown that the procedure of evaluating pressure losses in internally-heated piston-cylinder devices by assuming symmetrical friction is in error below ∼500°C.
Abstract: It is shown that the procedure of evaluating pressure losses in internally‐heated piston‐cylinder devices by assuming symmetrical friction is in error below ∼500°C. Previous results may be in error by as much as ∼5 kilobars at 40 kilobars and 25°C. A method of calibration is described which evaluates such unsymmetrical pressure losses.
TL;DR: In this article, a simple gating method for photomultipliers is presented, which has been found to be very useful in experiments of molecular physics where a weak spontaneous radiation to be detected is associated with a very intense pulse of stimulated radiation arising from a laser induced, coherent excitation of the medium.
Abstract: A simple gating method for photomultipliers is presented. The very high cutoff efficiency of the gate, its linearity, and the absence of spurious effect are shown by measurements taken on a RCA 7265 tube by using a pulsed and a cw light source in the S‐11 spectrum. This method has been found to be very useful in experiments of molecular physics where a weak spontaneous radiation to be detected is associated with a very intense pulse of stimulated radiation arising from a laser induced, coherent excitation of the medium.
TL;DR: Ionizing radiation effects on the dark current and noise pulse spectrum of photomultiplier tubes used in balloon and satellite X-ray observations were studied in this paper, where the effects of these effects were considered.
Abstract: Ionizing radiation effects on dark current and noise pulse spectrum of photomultiplier tubes used in balloon and satellite X-ray observations