Index of content:
Volume 25, Issue 5, May 1954
25(1954); http://dx.doi.org/10.1063/1.1771089View Description Hide Description
A new type of respirometer is described. The method involves a ``diver'' which is composed of a rigid respiratory chamber containing a CO2 absorbent and an O2‐containing collapsible sack feeding O2 into the chamber by way of a capillary tube. As O2 is used by the organism in the respiratory chamber, replacement O2 arrives from the collapsible sack thereby decreasing the buoyancy of the system. The change in buoyancy is recorded on a kymograph drum by an ink‐recording spring scale. The method has been put in practice using 50 ml Soxhlet distilling flasks with rubber stoppers penetrated by 27‐gauge hypodermic needles as the respiratory chamber and sections of Saran tubing (Visking Corporation of Chicago) with an O2 capacity of 40–50 ml attached to the stopper as the collapsible sacks. Recording spring scales with variable ranges from 2 to 20 g which have served satisfactorily for measuring natural variations in rates of O2 consumption for certain small animals are described.
25(1954); http://dx.doi.org/10.1063/1.1771090View Description Hide Description
A vortex burner has been developed that permits direct comparison of flamestability of fast‐burning and of slow‐burning gaseous fuels and their mixtures.
In this burner, air is introduced tangentially into a chamber to generate a vortex. The vortex is then accelerated by means of a converging nozzle which directs the air into a throat section where fuel is injected radially from ports in the periphery of the throat. The flame is stabilized in space in a divergent, pressure‐recovery section and burns as a whirling inverted cone.
Flamestability is independent of tangential velocity at any given air rate. However, changes in other parameters, such as throat diameter and length of the pressure‐recovery section, do have an effect on flamestability.
The results of these investigations with the vortex burner suggest that further studies with longer recovery sections are of interest. Likewise, the effect of gas temperature on flamestability will be studied.
25(1954); http://dx.doi.org/10.1063/1.1771091View Description Hide Description
A single crystal x‐ray spectrometer has been constructed in which the change in Bragg angle is effected through a linear rather than angular motion of the crystal. In certain measurement problems this design offers advantages over the conventional type from a standpoint of versatility and ease of alignment.
25(1954); http://dx.doi.org/10.1063/1.1771092View Description Hide Description
The spectroscopy of burning solid propellants has been generally limited to a photographic integration of the various flame zones as the burning strand is consumed and the flame passes a spectrographic slit. A few instances have been reported in which separation of the spectral emission from the different zones of the flame has been attempted, but the results are deficient either through loss of resolution of the spectrograph system or shortness of exposure time. An automatic constant level device is reported which now permits the isolation and detailed exposure of a definite flame zone throughout the complete time of burning of a 72‐inch length of strand. A discussion of the technique, illustrated with typical data on the degree of control, is presented. Typical absorption and emission spectrograms are given.
25(1954); http://dx.doi.org/10.1063/1.1771093View Description Hide Description
A magnetic deflector for the bevatron is described. Particles initially circulating at some distance from the deflecting field are caused to enter the field during the course of a single turn because of a small energy loss in a suitable placed target. The estimated efficiency is about 1 percent in.−2 at a detector located twenty feet from the circulating current.
25(1954); http://dx.doi.org/10.1063/1.1771094View Description Hide Description
The fundamental principles of electric fieldmeasurement by the use of inductors and vacuum tubeamplifiers are reviewed. An electric field meter is described that employs a rotating inductor and a synchronous ac generator to provide a sign responsive meter reading proportional to the electric field. The synchronized circuits eliminate moving contact rectifiers and promote calibration stability.
A simplified field meter using rectified inductorcurrents to operate a high‐impedance push‐pull bridge circuit is also described. Design features are incorporated in both instruments that permit them to operate continuously under unusually severe storm conditions.
25(1954); http://dx.doi.org/10.1063/1.1771095View Description Hide Description
Deuterons can be accelerated in the 184‐in. cyclotron to 190 Mev. To produce higher‐energy deuterons, doubly charged He3ions are accelerated to 493 Mev, and a fraction of them are stripped in an internal target, yielding deuterons with an average energy of 330 Mev. A current of 5×10−13 ampere is obtained in the experimental ``cave'' external to the cyclotron shielding. Range measurements indicate that these deuterons have an average energy of about 320 Mev.
The high cost of He3 necessitates an efficient gas‐recovery system. The exhaust from the cyclotron diffusion pump is passed through activated charcoal traps which are cooled to liquid‐nitrogen temperatures, and the gas that is not adsorbed (presumably helium) is returned to the cyclotron source. The loss from all causes is 0.8 cc/hour.
25(1954); http://dx.doi.org/10.1063/1.1771097View Description Hide Description
The results of an experimental study of the temperature dependence of commercial BF3neutron counters are reported. The arrangement used for this investigation is described and the results analyzed. The conclusion is reached that during a given pulse there is an increase in the number of negative ions formed by electron attachment with an increase in temperature of the tube. This effect is an equilibrium process. Upon reduction of the tube temperature the tube characteristics return to their original values. The consequence of this temperature dependence on the resultant counting rate is discussed.
25(1954); http://dx.doi.org/10.1063/1.1771098View Description Hide Description
A method has been developed to obtain an accurate estimate of the mean ionization of energetic, heavy charged particles using a device which has small stopping power. A sample of the frequency distribution of energy losses in each of n identical proportional counters is obtained. This information is treated by selecting the smallest of the n pulses and using this smallest pulse to represent the mean ionization of the particle. The experimental results are compared with Landau's theory of the statistical fluctuations in the specific ionization of charged particles.
25(1954); http://dx.doi.org/10.1063/1.1771099View Description Hide Description
An electronically triggered impulse generator has been developed which produces 20 kilovolt pulses having rise times of less than 0.6 millimicrosecond. When used with a shorting stub, this instrument produces delta‐function pulses of less than 2.5 millimicrosecond total width at full amplitude. The functions of primary pulse generation and pulse sharpening are separated. A special 50‐ohm coaxial switch was constructed of hydrogen thyratrons to produce 20 kilovolt primary pulses of arbitrary length and having rise times of less than 1.75 millimicroseconds. When triggered by a 2–500 volt pulse of 5 millimicroseconds rise time, the over‐all jitter of the system is of the order of 1 millimicrosecond.
25(1954); http://dx.doi.org/10.1063/1.1771100View Description Hide Description
A solar furnace is described, in which an array of many small plane mirrors is used to produce radiation of practically uniform intensity (up to about 5.5 cal/cm2 sec) over an area 5 cm square. This relatively large area of irradiation is required for experiments in which edge effects must be kept to a minimum, and could not have been obtained by means of a conventional continuously curved mirror of reasonable focal length and of moderate cost.
The performance of the segmented‐mirror furnace over a 15 month period is analyzed.
25(1954); http://dx.doi.org/10.1063/1.1771101View Description Hide Description
An error‐signal detector is discussed which can resolve relatively small signals with unusual broadband response and zero drift stability. An rf chopper principle replaces the more conventional mechanical choppers which have very limited band width. Circuit and mechanical construction details are discussed. Experimental performance shows resolution to 1 millivolt with a band width of at least 1 megacycle. A zero‐drift stability to 1 millivolt direct current is also readily attainable. Applications to high‐speed multichannel sampling and mechanical servos are discussed.
25(1954); http://dx.doi.org/10.1063/1.1771102View Description Hide Description
The Norrish‐Porter flash technique of ultraviolet spectroscopy has been adapted to the study of explosions induced by the thermal energy of the reacting gases at the temperature of mixing. The light emitted by the reacting gases during the induction period is used to actuate the flash source by means of a phototube and its associated electronic circuit. The concentrations of free radicals and other short‐lived molecular species can be studied as a function of time.
25(1954); http://dx.doi.org/10.1063/1.1771103View Description Hide Description
A computer has been constructed to sum Fourier series having up to 30 terms. Although this is a one‐dimensional computer it can be used for double and triple summations by using standard trigonometric expansions.
ODFAC sums electrically. The trigonometric function is produced by a variable‐angle transformer known as a resolver. Each amplitude is set by a variac which regulates the input to a particular resolver. The frequencies 2πnx for 31 values of n are arranged by gearing the rotors of the resolvers in ratios 0, 1, 2,…30. The resultant individual currents are added in parallel and the value at point x (in intervals of 1/60, 1/120, or 1/240 of a cell edge) is read on a voltmeter and the phase is read on an oscilloscope.
The relative speed of a computation is five to ten times faster than the standard strip methods. The average error in a computation compares favorably with the rounding‐off error in conventional two‐place strips.
25(1954); http://dx.doi.org/10.1063/1.1771104View Description Hide Description
Vacuum systems containing photographic materials may be most rapidly pumped if the materials have been desiccated previously. The primary factors influencing pumping time are the degree of preliminary desiccation and the amount of resorption of water vapor during the transfer of the material from the desiccator to the vacuum apparatus. Desiccation may be achieved by the use of a drying agent, evacuation, or the elevation of temperature. Resorption of water vapor may be minimized by rapid transfer of materials in tight containers from the desiccating means to the vacuum apparatus.
25(1954); http://dx.doi.org/10.1063/1.1771105View Description Hide Description
An arbitrary two‐dimensional magnetic field may be uniquely specified by listing all coefficients of the power‐series expansion of its complex potential function. An experimental procedure is described in which the first N coefficients are derived from an N‐point harmonic analysis of the radial component of field or gradient, as measured with a dipole or quadrupole search coil at N equally spaced angular positions about an arbitrary longitudinal axis. The method may be refined by mounting two coils coaxially on a radial arm, so connected as to balance out the strongest component present and permit more accurate determination of the higher harmonics. With four coils, odd or even harmonics also may be suppressed. Analysis of the symmetry of various magnet pole structures shows that many of the coefficients vanish identically. Procedures are outlined for measuring with a quadrupole search coil the five independent elements of the magnetic gradient dyadic at a point in an unrestricted field. It is shown that in the fringing region at the ends of a long magnet gap the axial average of the transverse field can be treated as a two‐dimensional field. It is correctly measured using line dipole or quadrupole search coils, whose design is prescribed. The procedure is identical with that for the two‐dimensional case. A further extension of the same method to measurements made with the electrolytic tray analog increases greatly their speed and accuracy.
25(1954); http://dx.doi.org/10.1063/1.1771107View Description Hide Description
The characteristics of a dc quadrupolemagnet have been measured using some of the techniques for measuring two‐dimensional fields and gradients proposed by W. C. Elmore and M. W. Garrett in the preceding paper. Saturation curves and measurements of the flux distribution in the magnet are presented. The characteristics of the magnet have been determined both in the interior and in the fringing region at each end. It is shown that by using a pole tip of circular cross section and correctly chosen radius it is possible to produce a magnetic field with gradient constant to ±1 percent out to 0.8 of the radius of the gap.
25(1954); http://dx.doi.org/10.1063/1.1771108View Description Hide Description
This paper describes an electronic instrument which has been developed for the measurement of internal friction to a high level of accuracy. The device is actuated by an input signal consisting of a voltage‐time decay wave form, with the necessary condition that the decay should follow an exponential law. The operation is both automatic and rapid so that the apparatus is suitable for investigating changes in damping when a given dependent parameter is varied.
25(1954); http://dx.doi.org/10.1063/1.1771109View Description Hide Description
An instrument is described which measures angles accurately and rapidly under the microscope. A mathematical model displays the principles involved. It is shown that accuracy is achieved with an ``optical lever arm'' which moves when the eyepiece rotates, the arm's being comparable to a 25‐cm mechanical arm attached to the outside of the eyepiece. Rapid measurements are possible by the reading of relative positions of the ``optical arm'' on an illuminated scale which appears superimposed over the microscope field of view. The design and limitations of a practical, working instrument are discussed.