Index of content:
Volume 29, Issue 7, July 1958
29(1958); http://dx.doi.org/10.1063/1.1716258View Description Hide Description
A heat transfer gauge suitable for measuring extremely high heat transfer rates under the quasi‐transient conditions occurring in shock tubes has been developed. The instrument is based on a calorimetric principle and is made possible by the short steady state times inherent in shock tubes. The technique developed extends, verifies, and supplements the shock tubeheat transfermeasurements made by thin film resistance thermometers.
The operating principles and experimental experiences with calorimeterheat transfer gauges are reported in some detail.
Much heat transfer data obtained with calorimeter gauges has been collected and published. Experimental measurements of laminar and turbulent heat transfer rates at velocities up to satellite speeds, approximately 26 000 ft/sec, have been reported. Heat transfer rates as high as 40 kw/cm2 have been encountered in these experiments.
29(1958); http://dx.doi.org/10.1063/1.1716259View Description Hide Description
A sintering process has been developed which makes it possible to utilize semiconductor material which comes in the form of small grains or small dendrite‐like pieces. When pressure, alternating current, and an rf field are applied, this loose material is sintered into rods without using a binder. These rods are used as ``feed'' for a floating zone apparatus.
29(1958); http://dx.doi.org/10.1063/1.1716260View Description Hide Description
An electron absorption spectrometer with an improved velocity analyzer using the principle of individually designed stages for deceleration, dispersion, and reacceleration is described. The instrument is usable over an energy range of 1 to 50 kev and can obtain angular distribution data over a range of ±0.1 radian. The angular resolution is better than 10−3 radian. The demonstrated energy resolution at 20 kev is 0.6 ev. This resolution appears to be limited by the primary beam energy spread which is characteristic of a beam produced by a telefocus gun with a tungstencathode.
29(1958); http://dx.doi.org/10.1063/1.1716261View Description Hide Description
An improved system for obtaining differential spectra from retarding potential measurements by the superposition of a small ac signal on the retarding voltage has been developed. The principal improvements are the choice of the point of injection of the modulation signal, the use of a low impedance preamplifier to improve the accuracy of the energy scale, and the use of a synchronous detector to improve the stability and reduce the effect of noise. The energy profile of a 15‐kev electron beam and the characteristicenergy loss spectra in collodion and aluminum have been measured. The quality of these measurements illustrates the over‐all performance of the present system.
29(1958); http://dx.doi.org/10.1063/1.1716262View Description Hide Description
A quartz crystal is placed in the feedback path of the marginal oscillator, between the cathodes of the oscillator tubes. This change results both in greatly improved frequency stability (2 parts in 107 per hour at 30 Mc with the simplest unthermostatted crystal) and a useful increase of signal‐to‐noise ratio (although not necessarily of noise figure) owing to the rf filtering action of the crystal. Magnetometer operation at an rf level as low as 100 μv across the sample coil, equivalent to an rf field of about 5 μgauss, has been obtained. A magnetservo based on the crystal‐controlled magnetometer is discussed.
29(1958); http://dx.doi.org/10.1063/1.1716263View Description Hide Description
Equipment for use with signal rise times slower than a millimicrosecond is readily available commercially. Recent advances in high‐energy physics have directed attention toward research in the fractional‐mμsec region. The fundamental tools for such research are pulse generators and oscilloscopes. Suitable pulse generators are commerically available, but suitable oscilloscope systems are not. There are two important factors that account for the lack of such oscilloscopes. One is that contemporary amplifiers are useless in the fractional‐mμsec region. The second is that output timing in commonly used trigger circuits is too sensitive to changes in input amplitude.
This paper describes an internally synchronized oscilloscope system utilizing commercially available components, which provides less than 2% signal reflection at the sync takeoff point, and has less than 5×10−12 second of sweep‐timing change per percent change in input amplitude (for amplitudes in excess of 30 trace widths).
29(1958); http://dx.doi.org/10.1063/1.1716264View Description Hide Description
An electronic spherometer is described, which has been used clinically for the measurement of uterine forces during obstetrical labor. The transducer, which is taped to the surface of the abdomen, senses change in the radius of curvature of the uterus, and sends a signal from a strain gauge bridge through an amplifier‐detector to a recorder. The instrument has been used to analyze muscular coordination of normal and abnormal labor.
29(1958); http://dx.doi.org/10.1063/1.1716265View Description Hide Description
The sensitive regions of several Freons in a bubble chamber have been determined. CF3Br, Freon 13B1, has been found to be sensitive at 30°C, at which temperature the equilibrium vapor pressure is only 264 psi. Because of its pleasant handling characteristics, and the fact that it can be used in any chamber designed for propane, it is suggested that it may find considerable use as a ``heavy'' liquid in large chambers. The time needed for bubbles to redissolve, and the difficulties implicit in the use of mixtures of liquids are discussed.
29(1958); http://dx.doi.org/10.1063/1.1716266View Description Hide Description
A recording electron paramagnetic resonance absorption spectrometer of very high sensitivity, operating at a wavelength of 3 cm, is described. It is of the reflection‐cavity‐in‐magic‐T‐bridge type, using a superheterodyne receiver. Its special features are: (1) a two‐cavity klystronoscillator with superior frequency stability and more available power; (2) a synchrodyne system to derive local oscillator power, thus avoiding the difficulty of tracking two independent oscillators; (3) a balanced magic‐T mixer which considerably reduces the noise output; (4) a double‐input low‐noise intermediate frequency amplifier at 30 Mc; and (5) a tunable high‐Q sample‐carrying cavity with an almost identical cavity to balance it in the magic‐T bridge. Arrangements for an oscilloscopic display of the absorption vsmagnetic field and a continuous recording of the derivative of absorption vsmagnetic field have been incorporated. Sensitivity of the microwave bridge system and of the spectrometer have been tested. About 1.1×10−11 mole of diphenyl picryl hydrazyl dissolved in purified benzene, which corresponded to approximately 1.06×10−14 mole of crystalline sample, has been detected by the spectrometer.
29(1958); http://dx.doi.org/10.1063/1.1716267View Description Hide Description
A circuit for pulse height discrimination in fast counting systems is described. Input pulses whose amplitude exceeds the threshold bias, adjustable from 1 to 21 volts, give rise to a positive output pulse of standard amplitude (6 volts), but length determined by the length of the input signal. Dead time is of order 20 mμsec and peaks 40 mμsec apart are handled independently.
29(1958); http://dx.doi.org/10.1063/1.1716268View Description Hide Description
In order to get information about the excitation processes in a discharge tube, a spectrograph has been built, which scans the range between the visible and the far ultraviolet. Using a Paschen‐Runge mounting the spectrum has been detected with a cooled E.M.I. photomultiplier, which can move along the Rowland circle with a velocity of 0.1–12 A per second. At the wavelength of 2500 A, 0.6 A could be resolved.
Combination Ion Chamber‐Proportional Counter Dosimeter for Measuring Gamma‐Ray Contamination of Neutron Fields29(1958); http://dx.doi.org/10.1063/1.1716269View Description Hide Description
A method for measuring low gamma‐ray contamination in a fast neutron field is described by which a single detector is operated sequentially as an ionization chamber and as a proportional counter. The range of collecting voltage for which the apparent gas multiplication is independent of particle type or mode of operation was determined. The method attains high accuracy in the measurement of the ratio of neutron to total dose and has been applied to several neutron sources.
29(1958); http://dx.doi.org/10.1063/1.1716271View Description Hide Description
An electronic circuit is described which permits the direct recording of a repetitive high‐frequency signal shown on the screen of a CRO by a common pen recorder. This is achieved by the intermittent connection of a condenser through a special type of gate to the Y‐deflection plates of the CRO, the gate being opened only during a very short time at a delay time Δt after the X‐sweep initiation. In this way the condenser is charged proportionally to the signal amplitude at the time Δt. If the voltage of this condenser is registered by a pen recorder, an exact copy of the signal displayed on the CRO screen will be obtained if Δt is slowly varied from zero to maximum sweep duration.
29(1958); http://dx.doi.org/10.1063/1.1716272View Description Hide Description
An ion source for pulsed operation has been developed which is based on producing a spark discharge between electrodes of a transition metal in which ordinary hydrogen or deuterium has been occluded. The beam consists principally of ions of hydrogen and of the electrode material. No neutral gas is evolved between pulses. High beam‐current densities have been obtained, both with axial and with radial extraction. Various methods have been devised for filtering out the heavy‐mass components of the beam.
29(1958); http://dx.doi.org/10.1063/1.1716273View Description Hide Description
Strain‐free cutting of metallic crystals at moderate rates can be obtained by localized electrochemicaldissolution using a wire cathode. The width of the attacked zone is limited by applying a protective plastic film. Clean sharp cuts cannot generally be expected.
29(1958); http://dx.doi.org/10.1063/1.1716274View Description Hide Description
Second‐order aberrations in mass spectrometers give rise to image broadening which is generally unsymmetrical about the optic axis, resulting in a net displacement of the image center from the optic axis. The net displacement depends on the properties of the mass resolving system and on the velocity and angular distribution in the ion beam. In the event different ionic species may possess either different mean kinetic energies or different energy distributions, the image shifts may differ appreciably, leading to small but appreciable errors in mass doublet measurements.
29(1958); http://dx.doi.org/10.1063/1.1716275View Description Hide Description
A thin‐film spherical conduction apparatus was designed and constructed for application to relatively viscous liquids such as hydrocarbon lubricants over a temperature range from ambient to −100°F and encompassing the solidification temperature. Freedom from the effects of convective heat transfer was demonstrated experimentally. The absolute accuracy of the measurements made with this instrument is believed to be within 2%.
29(1958); http://dx.doi.org/10.1063/1.1716276View Description Hide Description
By slowly modulating the quench frequency, the side‐band responses of a superregenerative spectrometer to a nuclear resonance can be prevented from appearing in a recorded spectrum. When searching for an unsplit Zeeman component in a nuclear quadrupole spectrum, an equivalent simplification of the recorded spectrum can be obtained by slowly modulating the magnetic field. Satisfactory spectrometers and the required modulation and compensation circuits are described.
29(1958); http://dx.doi.org/10.1063/1.1716277View Description Hide Description
All glass or predominantly glass vessels are well suited to spectroscopic or photochemical studies down to temperatures as low as 1.2°K. The choice of glass offers advantages of economy and simplicity in addition to allowing for a large degree of flexibility to be incorporated into a given design. A number of such Dewars are described and their relative merits discussed. It is shown that the heat leak arising from the optical arrangement is, in general, not serious.