Volume 38, Issue 10, October 1967
Index of content:
38(1967); http://dx.doi.org/10.1063/1.1720539View Description Hide Description
An earlier work on a Mattauch‐Herzog type mass spectrograph with a two‐stage electrostatic field is extended to investigating the conditions for simultaneous elimination of αβ and β2aberrations for all masses. In the course of study, the condition for obtaining a real image of ion source between two electrostatic fields is abandoned, and by this extension two series of solutions are found in neighborhood of φe 2=π/√2. The design parameters are numerically computed and tabulated for several examples. The α2aberrations are calculated and the total image defects are evaluated and found to be very small for a wide mass range.
38(1967); http://dx.doi.org/10.1063/1.1720540View Description Hide Description
A ring heat source probe has been developed for the rapid determination of thermal conductivity of rocks. In addition to the short period of time required to run the test (2–3 min), sample preparation is minimal, requiring only that parallel flats approximately two cm in diameter be cut or ground on opposite sides of the sample. A calibration chart can be provided with each probe so that thermal conductivity can be obtained from simple experimental data without elaborate calculation.
38(1967); http://dx.doi.org/10.1063/1.1720541View Description Hide Description
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.
38(1967); http://dx.doi.org/10.1063/1.1720542View Description Hide Description
An apparatus has been designed and built for scanning the surface of a semiconductor device with a light spot. The apparatus uses a modified commercial television set for the display of the photoresponse and a miniature CRT as flying spot source. Photoresponse pictures of lithium‐drifted siliconradiation detectors as well as of surface barrier type detectors are shown and interpretation is attempted.
38(1967); http://dx.doi.org/10.1063/1.1720544View Description Hide Description
A device for generating a fully‐ionized barium plasma column is described. It is similar to the previously described Q1 device except for the substitution of rhenium ionizing surfaces for tungsten, and barium for the alkali metals. The main motivation for the use of barium is that singly‐ionized barium has its resonance lines in the visible wavelength range, and thus allows the use of spectroscopic techniques for the determination of various plasma parameters. The special problems of barium in a Q device, and the spectroscopic techniques, including range of applicability and achievable accuracy of the measurements, are discussed.
38(1967); http://dx.doi.org/10.1063/1.1720546View Description Hide Description
Changes in the dark current and noise pulse spectrum of photomultiplier tubes due to ionizing radiations are reported. Tubes studied were the RCA 7265 and various versions of the ``ruggedized'' RCA 6199. Measurements were made both at 25°C and −40°C under exposure to 60Co γ rays, cosmic rays, 241Am alpha particles, and 90Sr β rays. All ionizing radiations incident on the phototube face were observed to produce additional dark current, and a considerable enhancement of the pulse spectrum, particularly at pulse sizes corresponding to several cathode photoelectrons. Each cosmic ray and interacting 60Co γ ray produced one large pulse, equivalent to about 10 single photoelectrons, and about 10 smaller pulses. The 241Am and 90Sr produced less than one noise event per incident particle. In order to explain the effects, three mechanisms seem to be required. Čerenkov radiation will produce the large pulses due to relativistic cosmic rays and Compton scatteredelectrons by 60Co γ rays. Scintillations in the glass with an efficiency of about 10 photons/MeV produce the effects due to the nonrelativistic alpha and β particles. It is suggested that phosphorescence induced by the short wavelength Čerenkov quanta can account for the many small pulses observed. These effects significantly alter the signal‐to‐noise characteristics of phototubes on balloons and satellites when applied to the detection of weak light sources, or low intensity x rays in the environment of space.
38(1967); http://dx.doi.org/10.1063/1.1720547View Description Hide Description
A technique for the measurement of velocity and strain of acoustic surface waves is proposed. It utilizes very thin vacuum deposited conductors in an applied magnetic field, which permits an unimpeded evaluation of the strain, velocity, and power of a propagating ultrasonicsurface wave. The proposed method of measurement is simple and accurate. An example of a 10 MHz surface wave on glass is utilized to illustrate the measurement of particle velocity and power density of the longitudinal component of the wave.
38(1967); http://dx.doi.org/10.1063/1.1720548View Description Hide Description
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− 2α½ kx (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 restorer. Peak‐to‐peak amplitude measurement of double‐differentiated signals performs, in effect, baseline restoration and, in addition, improves signal‐to‐noise ratio compared to peak‐amplitude measurement.
38(1967); http://dx.doi.org/10.1063/1.1720549View Description Hide Description
A magnetron cold cathode ion source (CCIS) has been developed for ultrahigh vacuum residual gas analysis. The purpose is to eliminate the spurious spectra produced by the conventional hot filament source and to obtain greater sensitivity. A commercial quadrupole mass analyzer was used to evaluate source performance and potential. Resolution equaled that obtained with a hot filament source, giving mass invariant peak separations, with 10% valleys, of 1.0 amu below 150 amu and 0.7 amu below 50 amu. Sensitivities exceeded those obtained with a hot filament source, operated at a 3 mA emission current, by factors of 1.5 to 4.6, depending on pressure and mass. The corresponding CCIS sensitivities, at 1‐amu peak separation, were 0.4 mA/Torr for mass 28 at 3×10−9 Torr and 1.2mA/Torr for mass 40 at 1×10−7 Torr. Experiments indicated a potential tenfold further sensitivity improvement if a quadrupole with a higher rf potential were used; by increasing quadrupole dimensions a still greater fraction of the source internal sensitivity, which is in the vicinity of 1 A/Torr, may be realized.
38(1967); http://dx.doi.org/10.1063/1.1720551View Description Hide Description
A modified mutual inductance bridge incorporating a commercial phase‐lock amplifier has been used to measure low temperature bulk resistivities in the range from 1 to 10 000 nΩ cm. No electrical contact is required with the spherical metal samples, so that possible heat leakage along electrical leads is eliminated, and measurements can be made below 40 mdeg Kelvin using a dilution refrigerator. The bridge circuit, capable of determining resistivity changes with a precision of better than 0.3%, is described.
38(1967); http://dx.doi.org/10.1063/1.1720553View Description Hide Description
An instrument is described which is a simple, accurate, reliable, and inexpensive device for continuously measuring and recording angular position or deflection. Incorporated in a torsion‐effusion apparatus it permits the visual observation of phase changes, deviations from molecular flow, and approach to equilibrium. The usual alignment problems associated with a lamp and scale are eliminated.
38(1967); http://dx.doi.org/10.1063/1.1720554View Description Hide Description
A new technique is described which provides for the study of x‐ray diffraction from a small selected region in the interior of a body. The method is of particular value for the measurement of interior elastic strain and will permit the complete evaluation of a triaxial state of stress. The collimation is appropriate for studies of either single crystals or polycrystallinematerial. Evaluations on single crystals of LiF with Mo Kα1 demonstrate that a conventional line x‐ray source provides useful diffracted power from a crystal volume of less than 10−4 cm3 located at a depth below the surface exceeding 0.3 cm. A strain reproducibility of better than 2×10−5 was attained in measurements at several depths in an unstrained crystal, and elastic strain evaluations were made through the thickness of a single crystal beam loaded in four‐point bending.
38(1967); http://dx.doi.org/10.1063/1.1720555View Description Hide Description
A spark chamber film reader has been developed which uses a computer directed cathode ray spot as the scanning light source. The equipment features data processing speed of 20 000 points per second while achieving position resolution of 4 μ. Search modes and film areas covered are controlled by the computer software giving wide flexibility.
38(1967); http://dx.doi.org/10.1063/1.1720556View Description Hide Description
The surface of a single crystal having etch steps of known heights can be used for magnification calibration. The etched basal surface of a hexagonal ferrite single crystal has etch steps whose heights are a precisely known function of its unit cell height. Depending upon the mixed‐layer stacking arrangement of the hexagonal ferrite phase such etch steps can have heights ranging in increments from 11.6 to 300 Å. After careful selection of a characterized hexagonal ferrite single crystal, it is etched in 1:1 HCl at 90°C until etch features are visible on the basal surface. The crystal is replicated by the one step method. The angle used for shadowing (from 1:1 to 3:1) must be accurately set since any error in the shadow angle will produce a corresponding error in the magnification. The shadow cast by the etch steps on the replica as viewed in the electron microscope is then used as the standard for calibration of magnifications in excess of 10 000 times.
38(1967); http://dx.doi.org/10.1063/1.1720557View Description Hide Description
Considerations for gravity gradiometer application have established the need for predicting gradiometer response to mass distributions of particular interest. A digital computer program has been developed to simulate the rotating gravitational mass sensor, and to map the gradient contours of the gravitational field created by an arbitrary mass distribution. This analysis demonstrates the interaction of the gradiometer with seond and higher order gravitational gradients. The information about the mass distribution of an object was found to increase with the gradient order. Considered in this study is the ``cruciform'' mass sensor, now being developed by Hughes Research Laboratories. This rotating gradiometer is theoretically capable of measuring the second, sixth, tenth, etc., order gradient. We are presently engaged in laboratory experiments which combine with these computer results in the understanding of gradient‐sensor interaction. This paper gives a basic introduction to gravitational tensors, followed by a mathematical formulation of the gradiometermodel.Computer results are included which demonstrate the gravitational gradient contours associated with some selected mass distributions.
38(1967); http://dx.doi.org/10.1063/1.1720558View Description Hide Description
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.