Index of content:
Volume 29, Issue 11, November 1958
29(1958); http://dx.doi.org/10.1063/1.1716061View Description Hide Description
This paper is concerned with sensing devices that may be used for thermal monitoring and control of modern aircraft propulsion units. Performance and service requirements that transcend some aspects of present flight requirements for such devices are described. The possibility of exploiting the pneumatic probe and the high‐temperature thermocouple to these ends is explored. Summaries are presented reviewing recent progress in the technical development of high‐temperature measurement by these methods.
Typical performance and thermoelectric behavior of twenty metallic thermocouples that have been calibrated above the melting point of platinum are presented. Seven of these pairs have been taken above 4000°F, and nine additional combinations have been calibrated above 3500°F. A comparison is made of the calibration atmospheres, maximum outputs, estimated maximum errors, temperature ranges of calibration, and ultimate temperature ranges for all thermocouples reported herein.
A review of methods of, and properties of refractory oxides suitable for thermocouple protection at high temperatures are presented. A qualitative intercomparison of these materials is made by ranking them according to relative merit of features desirable for thermocouple protection and insulation in the subject application.
Determination of the Magnetic Anisotropy of Single Crystals from Magnetic Torques Measured with Quartz Fibers29(1958); http://dx.doi.org/10.1063/1.1716062View Description Hide Description
The method of investigating the magnetic anisotropy of single crystals by observing the torque exerted on a crystal by a homogeneous magnetic field was found to be subject to several sources of error which were of particular importance when small differences of susceptibility were involved. Several changes in design of the equipment and in the experimental procedure have been introduced, resulting in a great improvement in the reproducibility of the measurements; these changes included the introduction of effective draft shielding, the use of high magnetic fields to saturate ferromagnetic impurities, and the use of a graphical method of data analysis. The method of determining the torsion constants of thin quartz fibers from the period of oscillation of a torsion pendulum has also been investigated; for accurate values it is necessary that the oscillating pendulum be under high vacuum and shielded from static electricity. A slight decrease in the torsion constants of quartz fibers left under tension for long periods of time has been observed. A systematic method of mounting and orienting the crystal specimens has also been devised.
29(1958); http://dx.doi.org/10.1063/1.1716063View Description Hide Description
An electron‐bombardment detector developed for the detection of noncondensable as well as condensable molecular beams is described. The ionization efficiency for a hydrogen deuteride beam is in the range of 10−5 to 10−4. Auxiliary components include: vacuum buffer chambers for source background gas reduction; a mass spectrometer for ion mass selection; an electron multiplier, electrometer, and phase‐sensitive detector combination for signal observation. Modulation techniques for beam and magnetic resonancedetection are discussed. Efficiencies, background problems, and relevant noise sources are included in a discussion of operational characteristics. A resonance line trace produced by at most 3% of a total HD beam is presented to demonstrate the signal to noise ratio at low signal levels. The system has effectively detectedbeams of permanent gases such as HD, D2, and Ne.
29(1958); http://dx.doi.org/10.1063/1.1716064View Description Hide Description
Second‐order focusing properties are considered for a nonuniform magnetic field with arbitrary circular boundaries in the case of normal entry and exit. The formula obtained here agrees with that obtained by Hintenberger for the special case α=β=0. It is also shown that the double and second‐order focusing can be achieved simultaneously. The numerical results are represented graphically for a symmetrical double‐focusing spectrometer with an arbitrary deflection angle.
29(1958); http://dx.doi.org/10.1063/1.1716065View Description Hide Description
A high‐speed spark light source is described which can be used in the photographic systems of shock tunnels, shock tubes, and ballistic ranges. The source provides five high‐intensity flashes, each with available delays of as low as 0.1 μsec between consecutive sparks. The transmission line principle is used with bariumtitanatecapacitors to obtain a spark discharge time of under 0.1 μsec. Five spark assemblies are mounted in line with a lens system to provide a common point where all spark flashes are brought to focus. The light source is used in conjunction with a high‐speed drum camera on which is mounted the recording film.
29(1958); http://dx.doi.org/10.1063/1.1716066View Description Hide Description
The design, construction, and operation of a displacement detector are described. In the operation of the detector the frequency shifts of two oscillators are observed; these frequencies depend on the separation distance of two probe capacitor plates from a third ground plate that is common to both of them. The circuitry and mechanical arrangement are such that two independent outputs are obtained; one is proportional to displacement normal to a surface and the other is proportional to displacement tangential to the surface. The calibration and testing of the device are described, and results of these tests are given along with displacement observations made on waves in a concrete surface. The detector is sensitive with good signal‐to‐noise ratio for displacements as small as 10−2 micron and with displacement frequencies as high as 105 cps, two components simultaneously.
29(1958); http://dx.doi.org/10.1063/1.1716067View Description Hide Description
An apparatus having up to four Po210sources suitable for radiation chemistry studies in liquids is described. Each unit consists of a source and housing that supplies a collimated beam of α particles, a variable speed stirrer, and an irradiation cell holder. Energy output is measured with the ferrous sulfate dosimeter.
29(1958); http://dx.doi.org/10.1063/1.1716068View Description Hide Description
A differential transformer with variable coupling placed at the tip of a catheter tube and surrounded by an umbrella type device has been used for the measurement of blood velocity. The instrument was carefully tested by means of a pump producing truly sinusoidal fluid movement. It was shown that the flowmeter has a linear characteristic and a linear frequency response with pump frequencies up to 25 cps. A blood flow recording taken in the ascending aorta of a dog with unopened chest demonstrates the instrument's practical application.
Microscope Mechanical Object Stage for the Study of the Tracks of Charged Particles in Photographic Emulsions or Other Objects in Transparent Media29(1958); http://dx.doi.org/10.1063/1.1716069View Description Hide Description
A new microscope mechanical object stage is described. In addition to the usual arrangements for measurements of the x and y coordinates for nuclear tracks in photographic emulsions, the stage is rotatable about the optical axis of the microscope as well as about an axis perpendicular to the optical axis. The angles of rotation can be read off scales. Through these arrangements and by the use of an eyepiece micrometer the orientation and the length of nuclear tracks can be measured directly.
Alternate Current Apparatus for Measuring the Ordinary Hall Coefficient of Ferromagnetic Metals and Semiconductors29(1958); http://dx.doi.org/10.1063/1.1716070View Description Hide Description
An apparatus is described for measuring the ordinary Hall coefficient of ferromagnetic metals such as Ni and of ferrimagneticsemiconductors such as Fe3O4. An alternating electric field at 1000 cps is used with a static magnetic field. The apparatus has a sensitivity of 10−18 watt, a noise level of 10−9 volt, and a voltage resolution of one part in 105. The sensitivity is required by the small ordinary Hall coefficient of the metals and the ferrites, and the resolution is needed to separate the ordinary and extraordinary Hall effects. The apparatus may be used with sample impedances ranging from less than one ohm to several thousand ohms. The sample holders which are an important part of the apparatus are described. The measurement technique is detailed as is a method for ensuring the absence of spurious voltages. The system may also be used to measure changes in other second‐order effects by bucking out all first‐order effects.
29(1958); http://dx.doi.org/10.1063/1.1716071View Description Hide Description
A tangentimeter for use with graphical data is described. Operation of the instrument is based on the production of multiple images by a coarse transmission grating. Under favorable conditions angular measurements may be made with a precision of ±0.1 degree.
29(1958); http://dx.doi.org/10.1063/1.1716072View Description Hide Description
A modification of the fine‐wire loop technique for studying surface contact resistances, as developed originally by Savage and Flom, is described. The principal change is substitution of quartz fiber for platinum wire as the resilient part of the probe. The contact end of the probe consists of either platinum or gold—other metals could be used as well.
An additional improvement is the provision for gradually increasing the applied force between the probe and surface at a low, known rate. This can provide information, not only on the electrical and physical durability of the film, but also on the changing bulk characteristics of the contact junction.
Applications in which the quartz fiber probe has been used for studying silver‐plated aluminum contacts, gold‐plated silver contacts, and copper‐Teflon films on copper are discussed.
29(1958); http://dx.doi.org/10.1063/1.1716073View Description Hide Description
The associated particle method of neutron detection has been used to reduce the background in measurements of the total cross section using neutrons from the D(d,n)He3reaction and to measure the time‐of‐flight of the neutrons that are inelastically scattered when elements are bombarded with T(d,n)He4neutrons. The techniques used are described.
29(1958); http://dx.doi.org/10.1063/1.1716074View Description Hide Description
A microcomparator illumination system is described which permits Rayleigh diffusiometer diagrams to be measured with increased precision. Measurement is based on the use of diffraction patterns generated by the Rayleigh diagram when this diagram is illuminated with point source, divergent, monochromatic light. Under favorable conditions a two‐ to fivefold increase in precision of measurement may be obtained with this illumination system.
29(1958); http://dx.doi.org/10.1063/1.1716075View Description Hide Description
A gas circulating system is described in which a sample undergoing thermal decomposition can be weighed continuously by means of a magnetic balance having a sensitivity of the order of 0.1 mg. Changes of composition in the gases contained in the system are determined by withdrawing samples directly into a mass spectrometer for analysis. Accurate quantitative measurements of the uptake and evolution of gases during the degradation process are thus obtained, providing an insight into the reactions that occur.
This simple system should prove useful in many other fields of investigation.
29(1958); http://dx.doi.org/10.1063/1.1716076View Description Hide Description
A portable instrument for measuringmagnetic fields and field gradients is described. The measurements depend on comparing the alternating emf's induced in two search coils oscillated synchronously at about 3 cps through angles of less than 3°, one in the field to be measured and the other in the reference field of a permanent magnet in the instrument. A precision Helipot is used as a potentiometer, in which a measured fraction of the signal from the reference coil is balanced against the signal from the probe coil. The null is obtained through an electronic amplifier and galvanometer. Tests of the instrument indicate 0.1% precision. A field gradient can be measured with the same instrument by use of a search coil which is given translatory oscillations in the direction of the gradient.
29(1958); http://dx.doi.org/10.1063/1.1716077View Description Hide Description
Anthracenesingle crystals ranging in thickness from 4 to 80 μ and from 0.5 to 2 cm2 in area have been prepared by crystallization from a selected solution system. The method is general and employs a density and temperature gradient within the solution which permits the crystal to grow while suspended in the solvent.
29(1958); http://dx.doi.org/10.1063/1.1716078View Description Hide Description
The various factors affecting the gamma‐ray energy resolution of NaI(Tl) scintillation spectrometers have been investigated experimentally with commercially packaged 2.5‐ and 5‐in. diam scintillators and routinely available 3‐ and 5‐in. photomultipliers. The resolution contains contributions from the scintillator light yield, photocathode efficiency, intrinsic resolution due to the material NaI(Tl) and two terms involving the effects of various spatial inhomogeneities in the packaged scintillator and photomultiplier. Insofar as possible these contributions are experimentally separated. The poorer resolution of the 5‐in. systems is in about equal measure caused by their smaller light yield, their larger spatial inhomogeneities and the lower efficiency of the 5‐in. photomultipliers in producing and collecting cathode electrons.
29(1958); http://dx.doi.org/10.1063/1.1716079View Description Hide Description
The impedance of a microwave cavity whose characteristics are time‐dependent, as caused for example by a contained gaseous discharge afterglow, can be examined by means of a frequency‐modulated search signal and a swept receiver. The intersection of the search‐signal frequency and the acceptance frequency of the receiver results in a pulse whose shape is sensitive to cavity resonance. The time of occurrence of the pulse depends upon signal‐to‐receiver phase. This in combination with the measured receiver dispersion allows measurement of reflection coefficient and frequency shifts smaller than the readability of a precision wavemeter at 10 kMc. Problems of oscillator tuning are mitigated and special stabilization procedures are eliminated. Only standard components are used.
29(1958); http://dx.doi.org/10.1063/1.1716040View Description Hide Description
A magnetic analyzer for nuclear reaction products has been built which employs a sector‐shaped uniform magnetic field. The shaped sectors are inserted in the 8.5‐in. gap of a C‐shaped magnet with a 12×12 in. cross section. The iron core is 54×33 in., and 69 360 ampere‐turns give 13 500 gauss across a total air gap of 1⅝ in. In the notation of W. G. Cross, [Rev. Sci. Instr. 22, 717, (1951)], the parameters were: ρ=15 in., φ=60°, useful gap=1.5 in., l′=22.5 in., l″=45 in., ε1=+46°38′, ε2=−18°21′, max usable α=±3°, max usable ω=±1.6°. The entrance boundary was straight, and the exit boundary had a convex curvature of 123.7 in. The boundaries of the sector and the locations of the object and image positions were corrected for the effect of the fringing field. The observed l″ was 46.5 in. Fringing field focusing in the direction perpendicular to the plane of deflection was not as strong as calculated; the maximum image height was 2 in. The magnet is capable of bending 12‐Mev protons and has an energy resolution of 300 for the maximum useful solid angle of 1/2000 of 4π steradians. The observed maximum energy resolution was 400. The advantages of this magnet are simplicity of construction and ease of adaptation to other sector parameters.