Volume 21, Issue 7, July 1950
Index of content:
21(1950); http://dx.doi.org/10.1063/1.1745660View Description Hide Description
The principles involved in the transfer of low boiling liquids under their own vapor pressures are indicated and calculations are presented for the specific case of the transfer of liquid nitrogen. A convenient device for transferring liquid nitrogen by this procedure is described and its operating characteristics are compared with the calculations.
21(1950); http://dx.doi.org/10.1063/1.1745661View Description Hide Description
An analysis is made of the focusing characteristics of a magnetic spectrometer having an annular magnetic field which varies approximately with 1/r ½, thus permitting axial as well as radial focusing of particles of a given energy. By considering the field angle and source location as independently variable, the analysis provides for an instrument more flexible in use than similar existing types.
An optical analogy is developed from which a first approximation to the field shape is made, and from which the source and image location, magnification, dispersion and resolution can be readily obtained. Information thus obtained, combined with the results of an investigation into the image shape based on a series expansion, through second order, of expressions for the field strength and particle coordinates, yields more detailed information on the field shape which gives optimum focusing conditions and resolution for any chosen set of initial conditions.
Comparisons are made with the homogeneous field spectrometer and with the spectrometer of Svartholm and Siegbahn.
21(1950); http://dx.doi.org/10.1063/1.1745662View Description Hide Description
A circuit for driving a long coaxial cable is described. Its response characteristics permit impedance matching of the coaxial line without sacrificing linearity of response, and make possible a relatively long line between the particle detector and the recording apparatus. The circuit was found to be reasonably stable for long periods of time, even under severe outdoor operating conditions.
21(1950); http://dx.doi.org/10.1063/1.1745664View Description Hide Description
Total radiated heat loss and average surface temperature of living bodies have heretofore required laborious computation from numerous local measurements. The present study introduces the blackbody principle for this objective. Shieldless surface receivers have been designed, and built from identical and symmetrical sets of thermoelectric foil junctions, which were then made different only in their power to absorb or reflect radiation. By means of thermal shunting, they have been rendered stable against air motion up to 8 m/sec. A cavity, when uniformly lined with such receivers, will integrate the measurements of radiated output into every direction of space, permitting a direct recording of the total. The receivers have been developed specifically for application to the human gradient calorimeter now under construction. However, since the laws of radiation apply to cavities of any size or shape, the proper function of blackbody radiometry could be experimentally verified with a smaller number of receivers in a body of 8×8×16 cu. in. The 4π‐measurement is practically independent of location, size, or shape of the emittent source. The sensitivity is 76 μv/cal./sec. Full response is attained within 2.4 sec.
21(1950); http://dx.doi.org/10.1063/1.1745665View Description Hide Description
This instrument produces, automatically, a curve of torqueversus angle of orientation for a thin iron or steel disk in a strong magnetic field. A resistance strain gauge converts the torque acting on the disk specimen to a small d.c. voltage, which is recorded on a ``strip‐chart'' recording potentiometer. The specimen is rotated in synchronism with the translation of the chart paper, both being driven by synchronous motors. A torque curve is completed in six minutes.
21(1950); http://dx.doi.org/10.1063/1.1745666View Description Hide Description
A new device for the distribution of vapors across an electron beam for molecular diffraction studies is described. The efficiency of the new method has made it possible to obtain molecular diffraction patterns with an electron microscope without need of alterations.
The vapors are ejected from a circular crest of a diffusion box immediately surrounding the beam to give a heavy concentration of vapors in contact with the beam while releasing a small amount of vapor. The method has been standardized with well known patterns of CCl4 and CBr4.
21(1950); http://dx.doi.org/10.1063/1.1745667View Description Hide Description
This paper describes apparatus for measuringinternal friction which satisfies the conditions (a) low induced stress amplitude to preclude any plastic flow of the specimen, (b) ability to install specimen within a few minutes after treatment, (c) rapidity of measurement, at a rate of ten to twenty per minute, (d) accuracy of at least one percent.
Longitudinal vibrations are induced by an eddy‐current drive, similar to one previously described in the literature, satisfying (a) and (b). Conditions (c) and (d) are obtained by measuring the decay time of free vibrations using vacuum tube trigger circuits and a counter chronograph. Satisfactory measurements can be made with push‐button rapidity and simplicity.
21(1950); http://dx.doi.org/10.1063/1.1745668View Description Hide Description
A series of experiments designed to yield information on the mechanisms of ultra‐high frequency discharges which influence the operation of ion sources employing such discharges is described. The main conclusions are that such discharges exhibit a high negative space charge due principally to secondary emission from the walls of the discharge chamber and that ion production is inhibited by the space‐charge trap so formed, that under certain conditions extremely intense electron beams may be obtained from a resonant cavity containing a gas discharge, and that fairly large ion currents may be obtained by the interaction of the emergent gas and the emergent electron beam in the exit orifice of the cavity.
21(1950); http://dx.doi.org/10.1063/1.1745669View Description Hide Description
An apparatus for the power stabilization of medium‐level microwave power sources, intended for laboratory use, by means of a degenerative feed‐back network connected in tandem with the power source is described. An analysis of the operation of the network is presented, based on obtaining optimum stabilizing action and optimum transmission efficiency for the network. Design of an electrically‐operated attenuator (which is a servo device), and its effect on the stabilization characteristics of the network are discussed. A transmission efficiency of 70 percent and a stabilization factor of 21 were obtained in an experimental model.
21(1950); http://dx.doi.org/10.1063/1.1745670View Description Hide Description
A recording fluxmeter has been developed which employs one or two integrators and a double element L and N Speedomax recorder for tracing magnetization curves directly on standard coordinate paper. The response of the recorder pen drive mechanism is proportional to the flux density, B, and is controlled by the B integrator. The response of the paper drive mechanism is proportional to the magnetizing force, H, and is controlled either by the magnetizing current, when the specimen is in the form of a ring, or by the H integrator when the specimen is in the form of a bar. Ayrton shunt networks provide flexible B and H scale adjustments. High accuracy and sensitivity are obtained by minimizing the causes of drift. At maximum sensitivity, four interlinkages give a deflection of one mm.
21(1950); http://dx.doi.org/10.1063/1.1745671View Description Hide Description
A variable space liquid absorption cell is described for use in the infra‐red spectral region. Its range of thicknesses from 5 mm to less than 10 μ makes it suitable for the compensation of absorption by solvents in a double beam spectrophotometer; its accuracy and reproducibility are sufficient for most direct qualitative and quantitative measurements. The minimum volume is approximately one cc, and the leakage is negligible. Its windows of rocksalt may easily be removed and repolished.
21(1950); http://dx.doi.org/10.1063/1.1745672View Description Hide Description
Measurements have been made on the time of decay of scintillations from organic phosphors irradiated with gamma‐rays. Interference between the output pulse from a photo‐multiplier and its reflection from a shorted line is used to determine the time constants.
21(1950); http://dx.doi.org/10.1063/1.1745673View Description Hide Description
In order to obtain a versatile instrument for directional cosmic‐ray studies, and to investigate an indicated correlation of the soft component of cosmic radiation with the present cosmic‐ray burst studies being carried on at the University of Colorado a dual cosmic‐raytelescope was constructed. Each bank of the telescope consists of five counter trays with nine Geiger counters in each tray. The electronic circuits are connected to give three triple consecutive coincidence trains: 1, 2, and 3; 2, 3, and 4; 3, 4, and 5. By the insertion of eight centimeter‐thick lead blocks covering the sensitive area of a Geiger tray between trays 3 and 4, and 4 and 5; a separation of the components of the radiation is possible.
The telescope is adjustable in zenith in 15 degree intervals from 0 to 75 degrees from the vertical. However, in azimuth, in order to investigate asymmetry characteristics, two positions 180 degrees apart are employed. The control of the telescope is entirely automatic with the recording of data being obtained by means of periodic photographs of the indicating panel, showing the counting rate, zenith and azimuthal positions, and the time and date of the measurement. The telescope changes in zenith and in azimuth every forty minutes; the changes in zenith and azimuth being displaced twenty minutes. A cycle of operation, which consists of the step change in zenith from 0 to 75 degrees with the associated alternate azimuthal changes, requires four hours.
21(1950); http://dx.doi.org/10.1063/1.1745674View Description Hide Description
A technique is developed for the rapid and precise measurement of the secondary electron emission properties of certain dielectricsurfaces. The dielectricsurface is bombarded by primary electrons having energies which produce a secondary emission ratio greater than unity. This establishes the surface potential at a known value. With the known potential difference between the dielectricsurface and primary electron source, the energies of the primary electrons are automatically determined for the first instant of surface bombardment. The net current to the dielectricsurface at any moment is measured by using a cathode‐ray oscillograph to observe the transient current to a metal plate which backs the dielectric. The method has been used to study metallic surfaces and has yielded results which agree very closely with those obtained using the conventional d.c. method of measurement.
21(1950); http://dx.doi.org/10.1063/1.1745675View Description Hide Description
In order to keep the width of cloud‐chamber tracks down to less than 1 mm the time delay between passage of a ray and completion of an expansion must be 10−2 sec. or less. When Geiger counter control is employed it may be difficult to obtain a sufficiently fast acting expansion control valve, particularly for a large cloud chamber. A valve combining a number of principles not all used by others has been constructed. By balancing pressures the movable valve parts can be made very light despite a large valve opening, and the controlling electromagnet can be quite small. Calculations were made concerning all the important design features. Even a small electromagnet must be laminated to insure sufficiently fast decay of its magnetic field. Most of the remaining time delay is caused by the aerodynamic resistance at the valve opening. For a valve diameter of 5.6 cm expansions are completed in 8×10−3 sec. With a power consumption of 0.17 watt a small vacuum tube is sufficient for operation. By balancing pressures one could construct a much larger valve operating as fast as the valve described with only a slight increase in power consumption.
21(1950); http://dx.doi.org/10.1063/1.1745676View Description Hide Description
By superimposing concentric radial elements on rectangular coordinate rulings, vernier systems may be constructed reading in two or three dimensions without the necessity of any particular angular orientation.
A two‐dimensional vernier may consist of one transparent element ruled with concentric circles. The observed tangencies of the circles, with regard to a rectangular grid placed in contact, provide the reading of the additional decimal of the coordinates of the fiducial center of the circles on the grid.
A three‐dimensional vernier system may be established by means of a binocular optical system presenting images of spheres concentric with the locating point and images of coordinate boxes in the same space. The tangency of a vernier sphere and coordinate plane indicates the last decimal of the reading.
Angular orientation may be indicated by radial lines near the points of tangency.
21(1950); http://dx.doi.org/10.1063/1.1745677View Description Hide Description
This paper describes a very simple low level coincidence circuit of moderate speed, which is suitable for use with two or more multiplier photo‐tubes in a scintillation detector of radiation. The operation of the circuit is analyzed, and performance data given to show its effectiveness in eliminating spurious counts due to noise pulses in the photo‐tubes. Some useful modifications of the circuit are suggested.
21(1950); http://dx.doi.org/10.1063/1.1745678View Description Hide Description
Shock waves close to the edge of explosive charges have been successfully photographed at rates exceeding 100,000,000 frames per second. These ultra‐high framing rates are obtained with a multislit focal plane shutter which is transported optically across the film plane by a rotating mirror. Linear shutter speeds up to 3000 meters per second are easily obtained, and the resulting framing rates with the proper selection of slit widths can be varied from 105 to 109 frames per second. Each individual frame is composed of a series of lines, and the degree of ``discontinuity'' across each frame is proportional to the total number of frames.
- LABORATORY AND SHOP NOTES
21(1950); http://dx.doi.org/10.1063/1.1745679View Description Hide Description