bluuebunny/crossref_metadata_2025 huggingface dataset:
Note on a Method for Measuring Small Electric Charges
Authors: Showers Ralph M.
Published: February 2005

A device for measuring electric charges of the order of 1.5×10−11 coulomb with a probable error of approximately one percent is described. The apparatus was designed to measure the ionization produced in air by roentgenographic apparatus. For that purpose the apparatus consists of two ionization chambers, an FP-54 electrometer tube, and an associated shielded switch. The grid of the electrometer tube is disconnected during the x-ray exposure. The shielded switch is designed to minimize drift in the plate current while the grid is floating and to minimize extraneous effects when the grid is connected successively to the two ionization chambers.
Electrodynamic Determination of the Magnetic Moment of Plates
Authors: Benedikt E. T.
Published: February 2005

An apparatus for the rapid determination of the magnetic moment of thin, circular plates of ferromagnetic material, uniformly magnetized in a direction perpendicular to their surface, is described. The method consists in rotating the specimen about a diameter near a fixed pick-up coil and compensating the voltage induced in the latter by varying the current in a suitable compensation coil which rotates with the same phase and speed as the specimen, in a position symmetrical to it with respect to the pick-up coil. From the value of the compensating current the magnetic moment of the disk can be calculated. The relation between the measured permanent moment and the magnetic properties of the plate material is discussed. It is shown that the method can be used for an approximate determination of the coercive force of the plate material.
Beryllium Windows for Permanently Evacuated X-Ray Tubes
Authors: Brackney Howard , Atlee Z. J.
Published: February 2005

The properties of beryllium which make it the ideal choice of material for windows used in transmitting long wave-length x-rays are discussed. Diffraction x-ray tubes of the permanently evacuated type using beryllium windows are described.
Slotted Cylindrical Rotors for Photometric Calibration
Authors: Platt J. R. , Clark H. E. , Cohen A. A. , Caldwell P. A.
Published: February 2005

Hollow cylindrical rotors with slotted walls can be used as substitutes for sector disks for some photometric applications. Designs are given of rotors which can replace a logarithmic sector, fixed sector disk, step sector, and variable sector disk. Some of these rotors may be used with non-parallel light. A rotor corresponding to a variable sector disk has been built with a variable slot which can be adjusted to several different openings while inside a vacuum system.
Determination of Optical Constants of Metals by Reflectivity Measurements
Authors: Collins J. R. , Bock R. O.
Published: February 2005

A method is described in which the reflectivity of linearly polarized light at various angles of incidence on plane evaporated samples of pure metals is measured throughout the spectral range from 4800A to 24,000A. By use of the electromagnetic equations describing the reflection process a graphical method for obtaining the optical constants from the data is worked out. The results are comparable in sensitivity and accuracy with other methods for certain limited ranges of the values of the constants.
On the Theory of the Electrostatic Beta-Particle Energy Spectrograph. III
Authors: Rogers F. T. , Horton C. W.
Published: February 2005

A study is made of the focusing action of the electrostatic analyzer (the electrostatic field between two concentric cylindrical-segment electrodes) on particles having relativistic speeds. A dependence of focal length on particle speed is derived; and its effects on the use of the analyzer for continuous spectra is examined. This study is an extension of a previous one of the same title in that: the central angle subtended by the electrode segments need not be 127° 27′, and the region of (relativistic speed) validity is somewhat greater.
Numerical Solution of the Boundary Value Problem for the Potential Equation by Means of Punched Cards
Authors: Kormes Mark
Published: February 2005

In this paper there is described in detail a method of obtaining numerical solutions of the boundary value problems for the potential equation ∂2u/∂x2+∂2u/∂y2=0 by means of punched cards. The differential equation is replaced by a finite difference equation and for a sufficiently fine net the value of the solution is assumed reasonably close to the known boundary values. These net point values are transferred onto punched cards and by repeated machine operations successive approximations are computed mechanically. When two successive approximations differ only in decimal places beyond the significant figure, the process is completed. A test example involving 145 net points required somewhat under 30 minutes of machine time per approximation. The method is suitable for use with standard I.B.M. or Remington Rand equipment.
An Inexpensive Stroboscope for High Speed Photography
Authors: Silverman Shirleigh , Warhus Wm. H.
Published: February 2005

A relatively inexpensive stroboscope of the Edgerton type for high speed photography has been built. A simple lamp of high light efficiency has been developed. Power requirements are of the order of 1 kva, and the parts are of the type found in most laboratories. Satisfactory photographs have been taken at rates up to 300 per second.
A Mass Spectrometer and Gaseous Thermal Diffusion Isotope Separator
Authors: Taylor James E.
Published: February 2005

A Nier type mass spectrometer is described in which the constant deflecting magnetic field is provided by a permanent magnet. An auxiliary magnetic field parallel to the electron beam in the ion source was found necessary. A six-tube gas thermal diffusion apparatus with convective coupling for concentrating heavy carbon is described. This compact unit (seven feet high) yields concentrations of C13 up to 20 percent. The concentration was observed as a function of time and the equilibrium concentration compared with theory for several pressures.
Studies on Double Refraction of Flow I. An Apparatus for the Study of Double Refraction of Flow at High Velocity Gradients
Authors: Edsall John T. , Gordon Charles G. , Mehl John W. , Scheinberg Herbert , Mann David W.
Published: February 2005

Observation in polarized light of a liquid moving between concentric cylinders, with a velocity gradient produced by rotation of one cylinder, permits determination of orientation of asymmetric molecules in the liquid. An apparatus with a gap of 0.25 mm between inner and outer cylinder is described; the inner, rotating cylinder is maintained accurately concentric with the outer cylinder at speeds up to 3000 r.p.m. or more, by a system of preloaded bearings which is described in detail. The cylinders are driven by a motor-generator system which produces adequate power and steady rotation over a wide range of speeds. Speed of rotation is determined stroboscopically, by a slight modification of the method of MacInnes. The optical system is briefly described, together with the methods for determining (1) the orientation of the optic axis in the flowing liquid, (2) the magnitude of the double refraction.
An Electronic Recording Flowmeter
Authors: Crittenden E. C. , Shipley R. E.
Published: February 2005

An instrument for measuring and automatically recording small steady liquid flows or the mean value of small pulsating liquid flows is described. The detecting unit employs a rotameter, or variable area meter, which consists of a vertical tube having a tapered bore in which a metal ``float'' is supported by the stream. Damping of motion of the ``float'' is obtained by means of an attached plunger whose cross-sectional area is slightly less than that of a chamber which communicates with the measuring tube. The position of the ``float,'' which varies almost linearly with flow, is determined electromagnetically with the aid of an electronic circuit and is optically recorded on moving sensitized paper. Interchangeable detecting units allow a wide range of flows to be measured. A detecting unit covering the range of 1 ml/min. to 200 ml/min. is described in detail.
A 21-Foot Multiple Range Grazing Incidence Spectrograph
Authors: Mack J. E. , Anderson E. E.
Published: February 2005

A 21-foot grazing incidence spectrograph, with wave-length ranges 0–470A and 0–2100A, is described. The use of a single photographic plate 154 cm long, coated on commercial polished plate glass, and a cylindrically ground cast plate holder, makes the dispersion curve smooth and close to the calculated one. Descriptions are given of the mechanical structure; the optical system and the method of focusing; and the electrical system, including a 3-μf, 70-kv condenser.
An Automatic X-Ray Diffraction Apparatus
Authors: Davey Wheeler P. , Smith F. Raymond , Harding Samuel W.
Published: February 2005

It is the purpose of this paper to describe a relatively simple x-ray diffraction apparatus which automatically records, in the form of an inked graph on a moving strip of coordinate paper, diffraction patterns made by substantially pure Mo K-alpha x-rays. A Mo-target x-ray tube is operated in the usual way on a half-wave rectified 60-cycle 42-kvmax circuit. Balanced filters of Zr and Sr are automatically inserted in the path of the incident beam during alternate ``useful'' half-cycles of the power circuit. The intensities of the two sets of diffracted beams are measured by a Geiger-Mueller quantum counter, one set of data is electrically subtracted from the other, and the difference (representing the pattern which would have been obtained from a pure Mo K-alpha beam), is automatically recorded in the form of an intensity vs. angle graph.
A Small Pressure-Insulated Electrostatic Generator
Authors: Jennings B. , Swartz C. D. , Rossi H. H.
Published: February 2005

The pressure-insulated electrostatic generator of the Physics Department at Johns Hopkins University is described in some detail. The generator was built at relatively small cost for work at about a million volts and has been used to accelerate protons for nuclear investigations.
Basic Solutions for Flow Measurement
Authors: Ziebolz H.
Published: February 2005

The purpose of this paper is to outline the conversion or translation of rate of fluid flows into movements, or, in simpler language—how to design a flow meter or flow indicator for fluid flows.
Four-Pi Solid Angle G-M Counters
Authors: Simpson J. A.
Published: February 2005

Two types of Geiger-Müller counters which count the particles in a solid angle slightly less than 4π are described. The use of thin metal windows permits their use with low energy β-particles. They are useful for small point sources or in determining the radioactivity of thin foils. Details of the construction are presented. A differential vacuum system for filling thin-window 4π counters is described.
A Magnetometer for the Determination of the Vertical Component of the Earth's Magnetic Field
Authors: Ting S. L. , Lin S. T.
Published: February 2005

The magnetometer consists mainly of two parts: a Helmholtz-Gaugain coil fixed on a horizontal divided circle for producing a uniform vertical magnetic field to balance the vertical component of the earth's field, and a magnet-balance system for observing the effect of the fields. The vertical component of the earth's field is determined in terms of the coil constants and the strength of the current passing through the coil. The error due to the horizontal component of the earth field and that due to the deviation of the center of gravity of the balance system from the rotating axis are eliminated, respectively, by taking the mean value of two observations with the axis of the balance set first in one direction and then turned into the opposite direction by rotating the whole instrument through 180° about a vertical axis, and by reversing the polarity of the balance. The special features of the instrument are as follows: (1) a pair of small solenoids is fixed inside the balance chamber and the balance can have its polarity reversed in its arrested position without being taken out; and (2) by providing another pair of horizontal coils on the chamber, the magnetometer serves at the same time as a galvanometer with the magnet balance as its moving magnet (the galvanometer is needed for the determination of the current and would otherwise be provided separately). By preliminary tests the instrument is found to give consistent results. Its sensitivity is about ½ min. per γ.
Theory and Use of Ross Filters. II
Authors: Kirkpatrick Paul
Published: February 2005

It is often advantageous to use Ross filters of a thickness much greater than that which has been judged to be optimum by the criterion of maximum pass-band transmission. The thicker filters show a larger ratio of measurable pass-band radiation to total spectrum power received and to received power resulting from balance errors. Prefiltration, though useful in connection with thin filters, confers no advantage when thick filters are used. Balance errors caused by the variation with atomic number of the function representing the variation of absorption coefficient with wave-length may, in principle, be eliminated at an indefinite number of chosen wave-lengths by giving one filter a particular type of thickness non-uniformity. Techniques for the construction and adjustment of Ross filters are described.
A Simple Autographic Stress-Strain Tester
Authors: Harris C. W.
Published: February 2005

A simple autographic stress-strain tester is described, which is connected to the test object by a single wire cable. The tester is small, has low inertia, and is most useful on compliant structures encased in refrigerators, ovens, or other inaccessible locations. It is suitable for testing textile cords.
A Copper Evaporation Method of Geiger-Müller Tube Construction
Authors: de Vos P. J. G. , Toit S. J. du
Published: February 2005

With the construction of larger BF3-tubes for use in cosmic-ray neutron research, the conventional tube construction making use of a brass cylinder enclosed with co-axial wire in a glass envelope becomes cumbersome owing to the large weight of the cylinder. A new method of construction, making use of the evaporation of copper in vacuum is described. Some of the characteristics of the new tubes are given together with an estimate of the time of discharge.
The Ellipsometer, an Apparatus to Measure Thicknesses of Thin Surface Films
Authors: Rothen Alexandre
Published: February 2005

An apparatus designed to determine the thickness of films deposited on metal slides is described. It is based on the measurement of the change that takes place in ellipticity of the light reflected after a slide has been coated with the film under investigation. The apparatus is capable of measuring a film thickness within ±0.3A, a sensitivity at least ten times greater than that obtained with the method based on light interference.
A Tympanometer
Authors: Kleiber Max
Published: February 2005

The instrument described measures the pressure of gases or liquids that cause bulging of an elastic membrane. The results are independent of the stresses in the membrane. The tympanometer is particularly adapted to measuring abdominal gas pressure, without injury to animals.
An Atmospheric Pressure Geiger-Müller Counter System For the Study of Respiratory Problems
Authors: Brown Sanborn C. , Good Wilfred M. , Evans Robley D.
Published: February 2005

An apparatus is described for using Geiger-Müller counters when the filling gas changes in composition during the observations with the counters. Two similar counters are used, one controls the voltage supply for both counters such that this ``control'' counter is always running at its threshold, independent of changes of its threshold voltage. The other, or ``measuring'' counter operates at a fixed voltage above its threshold, which may vary in the course of an experiment, and is used to measure activity of the gas circulating through it. Under these conditions a voltage plateau for the counters is not necessary. Linearity characteristics and reproducibility are found to be good.
Electron Diffraction Camera Viewing Screen and Photographic Plate Holder of Simple Design
Authors: Weber A. H. , Dahm Charles H.
Published: February 2005

The design and construction of a simple viewing screen and photographic plate holder for an electron diffraction camera is described. Ten exposures on a single 5×8″ plate are possible. There are no wax or grease joints.
Vacuum Tube Amplifier for Measuring Very Small Alternating Voltages
Authors: Roess L. C.
Published: February 2005

The design and construction of a low frequency vacuum tube amplifier capable of detecting 5·10−10 volt is described. The amplifier is intended to measure the alternating output of a rapid-response thermocouple in an infra-red spectrograph, the incident radiation being interrupted at frequencies between 1 and 5 hertz. (1 hertz=1 cycle per second.) The inherent noise level of the amplifier is less than the thermal noise of the thermocouple. This low amplifier noise level is attained by use of an excellent high gain input transformer, by careful selection of the first vacuum tube and operating its heater at low current, by use of inverse feedback, and by use of two power supplies, one for the heaters in series and a second for the plate and screen potentials, both of which have very good electronic voltage regulators. The noise level is further reduced by the use of inverse feedback and twin-T resistance-capacity networks to give a narrow and variable band width. The amplifier is operated from the a.c. power line. It feeds a short period galvanometer whose entire swing is recorded photographically so that the record has the appearance of a modulated carrier wave. A portable microammeter fed from a vacuum tube voltmeter is used as a visual monitor of the output. A simple photoelectric test signal generator is described, and typical records show the amplifier noise as well as its output for input signals as low as 6·10−10 volt. The effect of too narrow a band width on the recording time of an absorption spectrum is discussed briefly and is illustrated by water vapor spectrum records.
A Flow-Curve Recorder for a Rotational Viscometer
Authors: Weltmann Ruth N.
Published: February 2005

In the study of thixotropic substances and of materials of non-Newtonian behavior, it is important to obtain complete flow curves (rate of shear versus shearing stress) which are taken in accordance with a standardized procedure. The time interval for any given increase or decrease in rate of shear should remain constant. A recorder which draws complete flow curves has been developed as an attachment for a Couette type of viscometer. The deflection of the bob, which is proportional to the shearing stress, is plotted against the speed (r.p.m.) of the cup which is proportional to the rate of shear. For precise measurements the bob suspension spring must not be subjected to any friction load; therefore the recorder uses sparks generated by a high voltage to puncture the recording paper. The sparking electrode is moved by the bob deflection spring while the paper is moved perpendicularly to the electrode motion by the transmission handle, the position of which controls the cup speed. A number of measurements made with the recorder are shown. The recorded flow curves permit immediate interpretation and calculation (without any replotting) of the plastic viscosity, the yield value, and the thixotropic behavior of the tested materials. Also, a method is proposed for determining the plastic viscosity and the yield value at initial agitation, which are identified as ``the initial thixotropic viscosity'' and ``the initial thixotropic yield value.''
Mercury Jet Magnetometer
Authors: Kolin Alexander
Published: February 2005

Mercury is allowed to flow through a narrow non-conducting pipe provided with two pick-up electrodes at the ends of a diameter. In the presence of a magnetic field an e.m.f. is induced in the moving mercury. The potential difference detected between the electrodes is due to the component of the local magnetic field perpendicular to the pipe axis and to the diameter along which the electrodes are located. The device permits the establishment of the direction of the local field without introduction of a ferromagnetic body which might distort it. The magnetic field intensity in a sharply localized region can be determined. The instrument gives a direct reading proportional to the magnetic field intensity and lends itself to the study of rapidly varying transient fields as well as of constant ones. Fields of less than one oersted can still be easily detected. The magnetic field can be measured absolutely. Two ways of propelling the mercury are described. One of them utilizes gravity, and in the other method electromagnetic forces exerted upon a liquid conductor in a magnetic field are used.
Arc Ion Source with Direct-Current Filament Supply for 60-Inch Cyclotron
Authors: Cowie D. B. , Ksanda C. J.
Published: February 2005

A CAPILLARY arc ion source for a 60-inch cyclotron is described utilizing a direct-current filament supply. This has permitted 80-hour filament life with large deuteron beams. Stability of the arc and its operating conditions and construction are indicated.
A Cyclotron Beam Current Integrator and Recorder
Authors: Hamacher E. A.
Published: February 2005

The instrument described was developed to integrate and record the Massachusetts Institute of Technology Cyclotron beam current, for both the probe and the external target. Probe target currents are found by use of voltages developed by a thermopile which measures the temperature rise of the target cooling water; external target currents are measured directly by the voltage drop across a 10-ohm resistor, in parallel with the 10-ohm input impedance of the integrator itself, connected between the external target and ground. The instrument is essentially a stable, high sensitivity, linear a.c. amplifier, with a low impedance input, and a mechanical inverter for the d.c. input signal. Integration is accomplished by a standard a.c. watthour meter, and recording by means of a 5-ma, d.c. pen recorder. The amplified signal is also used to operate a warning system to indicate audibly a change in the beam current.
On Two Possible Modifications of the Induction Accelerator
Authors: Amaldi E. , Ferretti B.
Published: February 2005

Two possible modifications of the original Kerst induction accelerator are suggested, each of which allows one to double the energy of the electrons. The equation of the instantaneous circle, deduced by elementary considerations under rather general assumptions, is applied to different particular cases. The effect of the anharmonicities introduced by the magnetization curve of the iron is discussed; the different types of induction accelerators are compared with each other.
Continuous Wind Recorders
Authors: Ives Ronald L.
Published: February 2005

Field and station instruments to record one wind direction and two wind speeds on a single chart, over a wide range of wind speeds, and a very wide range of field conditions, are here described.
A Small Scale Hydrogen Liquefier
Authors: Fairbank Henry A.
Published: February 2005

A simple Hampson-type liquefier capable of producing about a liter of liquid hydrogen per hour is described. Compressed cylinder hydrogen is used avoiding the necessity of a compressor or gasometer. Design details of the heat interchangers and other vital parts are included as well as pertinent data on operation and performance.
Resonant Windows for Vacuum Seals in Rectangular Wave Guides
Authors: Fiske Milan D.
Published: February 2005

Resonant windows for vacuum seals of rectangular wave-guide sections are described. Theoretical and practical considerations are discussed. Design data are given permitting the construction of the windows over a wide range of resonant frequency and window band width. Particularly detailed data are given for windows in the 3-cm band.
Panoramic Mass Spectrometer Observation
Authors: Forrester A. Theodore , Whalley Wilfrid B.
Published: February 2005

In order to facilitate mass spectrometer observation, a low frequency scanning system was used to obtain mass-current curves on the face of an oscilloscope tube. The maximum sensitivity obtained was 5×10−14 amp. per cm vertical deflection. This was limited by the input capacity, the sweep frequency, and the available amplification.
A Constant Time Interval Reference Potential Indicator for Use with R—C Coupled Amplifiers
Authors: Kammer E. W.
Published: February 2005

A.c. amplifiers employing R-C coupling networks between stages are unsatisfactory for many applications which require the amplification of signals composed entirely or partially of low frequency or direct-current components. This paper describes a device applicable to an a.c. amplifier which permits the observation of signals composed of frequencies from zero to an upper limit imposed by the usual conditions for a.c. amplifiers.
A Fast Stress—Strain Machine
Authors: Dart S. L. , Anthony R. L. , Wack P. E.
Published: February 2005

A fast stress-strain machine for the study and testing of rubberlike materials is described. The machine is of simple design and can be operated at speeds up to 200 percent extension per second without serious error due to inertial effects. The complete stress-strain loop is recorded automatically. The reproducibility of the data obtained with this machine for a number of test specimens cut from the same tensile sheet is of the order of one percent.
High Speed Photography of the Cathode—Ray Tube
Authors: Goldstein H. , Bales Paul D.
Published: February 2005

Some techniques are described that have been developed for the periodic recording of single, fast traces on a cathode-ray tube at rates up to 4000 per second. The factors affecting the maximum writing speed are discussed, and it is shown that speeds as high as 70 cm/μsec. can be obtained without sacrifice of deflection sensitivity and using commercially available tubes and films. Several 16-mm cameras, adaptations of existing models, are described which permit photography of as many as 4000 traces per second. The film in these cameras moves continuously and at high speeds and cannot normally be projected as a moving picture. Where such projection is desired, a camera is employed which provides trigger pulses to initiate the transients synchronously with the film speed. Finally, a technique is presented for placing consecutive identification numbers in each frame area.
Thickness Measurement of Thin Coatings by X—Ray Absorption
Authors: Friedman H. , Birks L. S.
Published: February 2005

A method is described for determining the thickness of thin coatings on crystalline bases by means of an x-ray source and a Geiger counter, both situated on the same side of the coating. The x-rays pass through the coating and are reflected at a Bragg diffraction angle from the base, back to the counter, their intensity being reduced by absorption due to the double transmission through the coating. The thickness of the coating is computed from the measured absorption. The method is applicable to coating thicknesses in the range 10−5 to 10−2 centimeter.
A Reliable High Vacuum Gauge and Control System
Authors: Picard Robert G. , Smith Perry C. , Zollers Samuel M.
Published: February 2005

A new instrument for the measurement of vacuum is described. Two gauges are employed, one a thermocouple and the other a discharge gauge. The instrument is extremely satisfactory for the measurement of pressures in the range from atmospheric pressure to less than 10−4 mm Hg. Both gauges are of a type which will not be damaged if gases are suddenly admitted to the system. The gauges and power supply are described in detail. A circuit is given whereby the current from the gauges may be used to control equipment so that the pressure in the vacuum system may be used to operate other devices.
The Stabilization of X-Ray Tube Current and Voltage
Authors: LeMieux A. F. , Beeman W. W.
Published: February 2005

A simple and inexpensive degenerative electronic stabilizer which operates at ground potential in the primary a.c. line is described. Two such stabilizers maintain the current and voltage of a high wattage continuously pumped x-ray tube constant to about 0.1 percent. A low pass filter is used as a delay element in order to obtain high stabilization ratios without hunting. The operation of the stabilizer is not affected by 120-cycle a.c. components in the x-ray tube current, and transformer heating of the filament may be used.
Suppressed-Range Recording Peak Voltmeter
Authors: Brockman Frank G.
Published: February 2005

A recording peak voltmeter of the suppressed-range type is described. The minimum detectable voltage change is 10−3 volt, so that with an input of 10 volts r.m.s. average amplitude fluctuations of 0.01 percent can be recorded.
Range Extender for General Radio 760A Sound Analyzer
Authors: Cobine J. D. , Curry J. R.
Published: February 2005

This attachment extends the range of the GR 760A sound analyzer to one megacycle by means of an oscillator and a tuned mixer which beat high frequency signals down to a frequency accepted by the analyzer. The apparatus is easily constructed, simple to operate, and has proved to be both reliable and flexible. This article describes the circuits and physical arrangements, and discusses the calibration and use of the attachment in the study of high frequency noise spectra.
An Apparatus for Recording Pressure on a Spectrographic Plate
Authors: Crawford Bryce L. , Huggett Clayton
Published: February 2005

A simple device for recording pressure on a spectrographic plate, simultaneously with the recording of the spectrum itself, is described. This permits following both the absorption spectrum and the pressure of the gas in a reaction cell, as functions of time. Conditions are given which will insure an approximately linear pressure scale.
A Megavoltmeter for Induction Electron Accelerators
Authors: Westendorp W. F.
Published: February 2005

A direct reading instrument is described for showing the electron voltage to which the induction electron accelerator is adjusted in correlation to operating voltage of the machine and phase of the orbit shift circuit.
Laboratory Pulse Generator with Variable Time Delay
Authors: Scheuch D. R. , Cowan F. P.
Published: February 2005

A laboratory pulse generator, in which the output pulse occurs at a controllable time interval after an input signal, is described. The delay is obtained by means of a ``flip-flop,'' or biased multivibrator, and is adjustable from 2 to 850 microseconds. The width of the output pulse is adjustable from 1 to 40 microseconds. An input signal of arbitrary wave form may be used at frequencies up to 100 kc per sec. Pulse or high frequency sine wave inputs of 0.2 volt or more will operate the instrument while larger input signals are required for sine waves of lower frequency. The delayed pulse is delivered at low impedance with a maximum amplitude of 150 volts. A negative synch. output pulse, coincident with the start of the delay, is provided. Possible modifications and simplifications suitable for special applications are discussed.
Microtomy with a Reciprocating Circular Knife and a Mechanism for Sharpening the Knife
Authors: Heard Osborne O.
Published: February 2005

The use of a circular reciprocating microtome knife is described along with a mechanism for sharpening the knife. A reduction of distortion in serial sections for embryological reconstructions is claimed and the physics involved noted. Related subjects are discussed and special emphasis is placed on the mechanics of sectioning with such a knife. The procedure of generating and finishing the knife facets is briefly outlined and compared with those used in sharpening straight microtome knives.
Small Mica Window Geiger-Müller Counter for Measurements of Radioactive Isotopes in Vivo
Authors: Strajman Enrique
Published: February 2005

A small Geiger-Müller counter model constructed for the purpose of studying in vivo the metabolism of beta-particle isotopes in normal and pathological tissues is described. A ballast bulb was added to the small Geiger counters, thus increasing the volume of argon-alcohol mixture which appears to prolong the life of the counter.
An Automatic Sample Changer to Be Used for Measuring Radioactive Samples
Authors: Peacock Wendell C. , Good Wilfred M.
Published: February 2005

A sample changer used in the routine measurement of large numbers of radioactive samples is described. It has been used with a scaling circuit and an interval timer for single tracer experiments and with counting rate meters for double tracer experiments. Circuits and methods of preparing samples are included.
Design of Beta-Ray and Gamma-Ray Geiger-Müller Counters
Authors: Good W. , Kip A. , Brown S.
Published: February 2005

Every laboratory working in the field of radioactivity, develops many types of Geiger-Müller counters. From time to time, many groups have published descriptions of well-tested examples of counters, which have met certain requirements with particular success. This paper describes three types of counters which have proved particularly useful in this laboratory. These are the mica window, bell-type beta-counter, a modified bell-counter used as an x-ray counter, and a high sensitivity bismuth screen gamma-counter of conventional design.
Mechanical Frequency Modulation System as Applied to the Cyclotron
Authors: Schmidt F. H.
Published: February 2005

A high speed variable capacitor operating in a vacuum is described. The capacitor is coupled to the cyclotron dee by means of a transmission line whose length is such that a voltage node occurs near its center. The frequency change obtained is greater than 13 percent. The frequency-time characteristic of the system is considered and a method of adjusting the shape of the characteristic is described.
Current Integrator
Authors: Watt B. E.
Published: February 2005

An integrator for the current range from 50 microamperes to below 4 × 10−9 ampere has been developed. The charge per count is constant to within two percent over the entire range, and is unaffected by power supply variations.
An Automatic Recording Gamma-Ray Spectrometer
Authors: Strickler Thomas D. , Wadey Walter G.
Published: February 2005

A scintillation spectrometer making use of a large NaI/TlI crystal mounted on an RCA 5819 photomultiplier tube has been constructed. It was designed for the high efficiency counting of gamma-rays in the energy range 0.5–1.5 Mev. Techniques used for crystal mounting and assembly of apparatus have proved very satisfactory for prolonged operation. Additional components have been provided for automatic recording of data.
A New Type of Heat Interchanger for Large Liquefiers
Authors: Nicol J. , Smith T. S. , Heer C. V. , Daunt J. G.
Published: February 2005

Details are given of the design and performance of a heat interchanger suitable for transfering heat from a gas of high heat content per unit volume to one of low heat content per unit volume. The interchanger is suitable for use in large liquefiers, and a report is given of its performance in a helium liquefier giving 6.5 liters of liquid helium per hour. The construction is simple and involves no techniques not already available in an average laboratory workshop. A close correlation is reported between the computed and observed efficiencies and pressure drops in these interchangers.
Radial Oscillations in the Cyclotron
Authors: Hough P. V. C.
Published: February 2005

The excitation and evolution of the radial oscillations of ions in the cyclotron has been studied theoretically and experimentally. A simple method for calculating the pattern of the oscillations leads to detailed criteria for the preparation of the magnetic field and a systematic theory of shimming. A new method for measuring the pattern of the oscillations is used to check the theory. The results are applied briefly to the problem of beam extraction.
A Photometer and Absorption Cell Attachment for Ultramicro-Spectrophotometry
Authors: Craig R. , Bartel A. , Kirk Paul L.
Published: February 2005

A cell holder and photometer for use with the Beckman Model DU spectrophotometer is described. The cell holder is designed to position capillary cells of small diameter, e.g. 0.7 mm and 5 cm in length in the narrow beam of light passed through fine collimating masks. The capacity of the cells is about 20 mm3 which allows analysis of quantities about 10 times smaller than have been hitherto analyzable. The photometer employs a multiplier phototube in order to achieve the requisite sensitivity for the small amount of light transmitted.
The Regular Production of 85 Percent Para Liquid Hydrogen
Authors: Grilly E. R.
Published: February 2005

The storage of liquid hydrogen has become much less troublesome as a result of regularly producing 85 percent para-liquid instead of ``normal.'' An ordinary liquefaction plant was modified so that the ortho- to para-conversion is catalyzed in the feed gas (at 76°K) and in the liquid within the liquefier. The liquid-phase conversion causes the full liquefaction rate to drop from 25 to 20.5 liters/hour. Data were also obtained for other liquefaction rates, with and without feed-gas catalysis.
Extrapolation Chamber for the Measurement of Beta Sources
Authors: Loevinger Robert
Published: February 2005

Construction and operation of a variable-spacing, parallel-plate ionization chamber is described. It has been designed for the measurement of beta-particle sources of medical and biological interest. It has concentric collecting electrodes of 1, 3, 10, and 30 mm diameter. The air gap in which ionization is measured can be adjusted from 0.04 to 10 mm. Ionization current is measured with a commercial vacuum tube voltmeter which has a full scale sensitivity of 2×10−13 amp. The instrument sensitivity is about 0.4 esu/cc-sec using a one mm diameter collecting electrode with a collecting air gap of 0.2 mm, and about 4×10−5 esu/cc-sec using a 30 mm diameter collecting electrode with an air gap of 2 mm. Conditions are described in detail for the determination of ionization per cc in vanishingly small air gaps between polystyrene electrodes, with an accuracy of a few percent.
Gamma-Ray Measurements by the Magnetic Analysis of Compton Electrons
Authors: Motz J. W. , Miller William , Wyckoff H. O. , Gibson H. F. , Kirn F. S.
Published: February 2005

A magnetic spectrometer has been constructed which can be used to determine photon intensities and energies over an energy range of approximately 0.2 to 12 Mev. Over this energy range, the detection efficiency of the spectrometer is such that a monoenergetic photon flux density of the order of 105 photons per cm2 will produce one count. The instrument measures the momentum distribution of Compton electrons ejected from a thin beryllium foil into a small solid angle in the direction of the incident photon beam. A method of converting these measurements to corresponding photon intensities and energies is presented. The calculations necessary to convert to photon intensities are based on the Klein-Nishina formula, and include the effects of scattering and energy loss of the electrons in the foil.

The spectrometer was calibrated from (a) the line shapes produced when the gamma-rays from the radioactive sources Cs137 (0.661 Mev) and Na24 (1.37 Mev, 2.76 Mev) were incident on the foil, and (b) the intensity measurements of these sources, obtained with an ionization chamber.
Method for Obtaining Streaming Orientation and Simultaneous Determination of Dielectric Properties in Macromolecular Solutions
Authors: Jacobson Bertil
Published: February 2005

A method has been devised for the measurement of the dielectric constant and the specific conductance of aqueous solutions undergoing streaming with velocity gradients between 0 and 10 000 sec−1. The solution to be investigated is placed in the annular space between two concentric cylinders forming the measuring cell. Electrodes are inserted in the walls of the cylinders of which the outer is fixed and the inner is rotated. Two types of cells are used; the electrical field in one case being perpendicular to and in the other case parallel with the stream lines. The impedance of the cell with the solution investigated is determined with a specially constructed Schering bridge making measurements possible in the frequency range 0.05 to 5 megacycles per second and at specific conductances of 1 to 200 μmho per centimeter. The advantage of the bridge circuit employed is that the conductance of the cell is balanced by a variable air condenser, making possible an accuracy of 0.1 percent in the values for both conductance and dielectric constant. Excellent mechanical and electrical stability and a low interference level are necessary for high accuracy. Experiments with solutions of sodium thymonucleate show that the current interpretation of the dielectric properties of macromolecules must be revised. The term streaming dielectric investigations is suggested as a suitable name for studies with the type of instrument described.
An Integrating Photometer for X-Ray Intensity Measurements
Authors: Alexander E. , Fraenkel B. S. , Many A. , Steinberger I. T.
Published: February 2005

X-ray diffraction spots on films vary in area and are uneven in density. An instrument is described, which, after calibration against a standard intensity scale imprinted on the film, scans the spot by a light ray, and transforms transmitted light pulses into linear functions of intensity by electronic means. A figure, proportional to the intensity of the spot, is obtained on a mechanical counter. The integrating process is fully automatic, and measurement of one spot takes about a minute. Reproducibility depends on the relative intensity of the measured spot, and can be raised up to 1 percent.
Development of a High-Fidelity Preamplifier for Use in the Recording of Bioelectric Potentials with Intracellular Electrodes
Authors: Solms S. J. , Nastuk W. L. , Alexander J. T.
Published: February 2005

In the intracellular recording of action potentials, the fidelity of recording is limited by the resistance and capacitance of the ultramicroelectrode required for making connection to the intracellular contents, and by the characteristics of the input circuit of the amplifier. The cathode follower circuit conventionally used to minimize the time constant of the recording system is discussed and its shortcomings are analyzed. An improved circuit involving positive feedback is presented. The measurement of the recording system time constant is discussed.
A Method of Describing the Detectivity of Photoconductive Cells
Authors: Jones R. Clark
Published: February 2005

A simple method is proposed for describing the detectivity of photoconductive cells.

First it is pointed out that at signal modulation frequencies well below the frequency that corresponds to the time constant of the cell, the responsivity of the cell is independent of the frequency. For the same range of signal modulation frequencies, the noise power (mean-square noise voltage) per unit frequency bandwidth is inversely proportional to the frequency. It is a very general property of radiation detectors obeying Lambert's law that the detectivity varies inversely as the square root of the sensitive area.

As a result of the facts just stated, one is led to the conclusion that if one multiplies the measured detectivity by the square root of the cell's sensitive area and by the square root of the band width of the noise, and if one divides by the square root of the frequency of the test signal, one obtains a result that is independent of the test band width and test frequency and is independent also of the sensitive area of the cell. The detectivity 𝒟 so obtained is defined in Eq. (3) and is called the ``detectivity in the reference condition C.''

The detectivity 𝒟 is not proposed as a replacement for a detailed description of the test conditions and test results. It is an auxiliary quantity to be computed from the test results. It has the advantage over any other single test result that the knowledge of it alone permits a direct and significant comparison of two cells, even though the cells are of different area and are tested under different conditions.

A discussion is included of the various auxiliary ``ground rules'' that must be observed if one wishes to state the detectivity of a cell with complete unambiguity.
Deterioration of Boron Trifluoride Counters Due to High Counting Rates
Authors: Soberman Robert K. , Korff Serge A. , Friedland Stephen S. , Katzenstein Henry S.
Published: February 2005

Twenty-two boron trifluoride counters were run at counting rates of about 106 counts per min in the proportional region until they had all lost their plateaus of voltage versus counting rate. This occurred in from 108 to 109 counts. The pulse heights decreased to the point at which maximum sensitivity of the circuitry failed to record more than 103 counts per min, although many more small pulses could be detected on an oscilloscope. Raising the voltage did not restore the pulse heights. The counters did not recover after inactive periods of up to four months. Gas samples from several of the counters were analyzed on a mass spectrometer. A theory is proposed which would explain the deterioration on the basis of a negative ion sheath which is formed when the BF3 dissociates.
Magnetic Pumps for Corrosive Gases and Liquids
Authors: Rosen F. D.
Published: February 2005

Small, completely sealed, magnetically operated pumps have been constructed for use in circulation of corrosive gases. Successful and extended use has been obtained with gases such as uranium hexafluoride and hydrogen fluoride at pressures up to 175 psig and 100°C. Pumping characteristics with respect to air at atmospheric suction pressure are given.
An Anticoincidence Gamma-Ray Scintillation Spectrometer
Authors: Albert Richard D.
Published: February 2005

A new type of scintillation spectrometer is described. It is designed to suppress signals arising from incident photons that are not completely absorbed in the primary detecting NaI(Tl) crystal. When an undesired signal is detected by means of a cluster of NaI(Tl) crystals surrounding the primary crystal, it is removed through the discriminating action of an anticoincidence electronic gate. Under conditions of good discrimination, this type of arrangement offers the advantage of yielding the gamma-ray spectrum directly without any interpretation of results which might become laborious, particularly if the incident gamma radiation has a complex spectrum. Results are presented that illustrate the discrimination action of the device by means of photographic representations of the scintillation gamma-ray spectra of Cs137 and Na22.
A Phototube Measuring Circuit for Thermopiles
Authors: Brinton R. K. , O'Konski C. T.
Published: February 2005

A recording system is described which measures the electromotive force generated by slowly responding linear-type thermopiles. A means is provided for compensating electrically for the zero signal drift so that the thermopile may be used conveniently under rather unstable thermal surroundings. A twin phototube arranged in a feedback type amplification circuit is used as a receiver for the light beam reflected from the mirror of a sensitive galvanometer connected in series with the thermopile. The current from the feedback circuit which automatically keeps the galvanometer essentially at its zero signal position is directly proportional to the thermopile signal. This current may be measured by a conventional microammeter or an automatically recording meter if desired.
A Compact Rear-Illumination System for Cloud Chambers
Authors: Cowan E. W.
Published: February 2005

The use of cylindrical mirrors made of bent plate glass results in a rear-illumination system for cloud chambers that is compact and gives good contrast with more than adequate light intensity. A small balloon-borne cloud chamber using this system requires only 6 j of energy for the light, using a lens opening of f/40. The mirrors are made in an inexpensive way from plate glass by heating the glass and allowing it to sag into a mold of the proper shape.