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Showing papers in "Review of Scientific Instruments in 1946"


Journal ArticleDOI
TL;DR: The experimentally measured root mean square fluctuation of the output meter of a microwave radiometer compares favorably with a theoretical value of 0.4°C, which corresponds to a minimum detectable power of 10-16 watt.
Abstract: The connection between Johnson noise and blackbody radiation is discussed, using a simple thermodynamic model. A microwave radiometer is described together with its theory of operation. The experimentally measured root mean square fluctuation of the output meter of a microwave radiometer (0.4°C) compares favorably with a theoretical value of 0.46°C. With an r-f band width of 16 mc/sec., the 0.4°C corresponds to a minimum detectable power of 10-16 watt. The method of calibrating using a variable temperature resistive load is described.

941 citations


Journal ArticleDOI
TL;DR: Two circuits for use to control the frequency of a microwave oscillator by an external high Q cavity are described, and a technique by which the frequency‐stabilization systems could be used to investigate the structure of microwave absorption spectra is suggested.
Abstract: Two circuits for use to control the frequency of a microwave oscillator by an external high Q cavity are described. One of the circuits uses a microwave equivalent of the frequency discriminator, in conjunction with a d.c. amplifier. The other uses the cavity in a special circuit that provides an intermediate‐frequency signal that is a measure of the difference between the frequencies of the oscillator and cavity. This allows the use of an intermediate‐frequency amplifier. The resulting stability of the oscillators is such that audible beat frequencies can be produced between two oscillators at 10,000 Mc/sec. The resultant signal can be frequency modulated at audiofrequencies, with stabilization acting throughout the modulation cycle. A technique by which the frequency‐stabilization systems could be used to investigate, with high resolution, the structure of microwave absorption spectra is suggested.

428 citations


Journal ArticleDOI
TL;DR: Six proposed devices for the production of charged particles with energies greater than 200 Mev are described briefly and some results of radiative energy loss by fast charged particles are presented.
Abstract: Six proposed devices for the production of charged particles with energies greater than 200 Mev are described briefly. These are: betatron, synchrotron, microtron, linear resonator accelerator, linear wave guide accelerator, and relativistic ion cyclotron. Attractive features and possible difficulties are discussed in each case. An Appendix presents some results of the theory of radiative energy loss by fast charged particles.

100 citations


Journal ArticleDOI
TL;DR: The amplifier is compact and rugged, and it is not affected by vibrations or accelerations experienced in moving vehicles, and is employed in the measurement of radiant energies in infra‐red spectrographs and for various laboratory and field measurements.
Abstract: The electronic amplifier, described herein, is designed to measure extremely small d.c. and low frequency a.c. voltages in low impedance sources. Expressing the electrical noise in terms of equivalent input voltage with a 5‐ohm input resistance and a 5‐milliamp. Esterline‐Angus recorder, the maximum departure from the mean does not exceed 1.5×10−9 volt. Under laboratory conditions the drift is less than 5×10−9 volt over a period of 8 hours. The amplifier is compact and rugged, and it is not affected by vibrations or accelerations experienced in moving vehicles. At present the amplifier is employed in the measurement of radiant energies in infra‐red spectrographs. It is also used for various laboratory and field measurements.

62 citations


Journal ArticleDOI
TL;DR: Two forms of a high speed type of microtome are described which are able to cut cross sections to the thinness required for electron microscopic study (0.1 to 0.8 micron, depending on the material).
Abstract: Two forms of a high speed type of microtome are described which are able to cut cross sections to the thinness required for electron microscopic study (0.1 to 0.8 micron, depending on the material). Techniques of microtome operation are suggested together with a few methods of sample preparation and subsequent section treatment, namely, collecting, selecting, and mounting. Embedding materials which sublime readily are described; these have been used successfully with this high speed microtome to support many types of materials. These volatile embedding materials have the advantage that they eliminate the difficulties that on some occasions arise with the use of solvents in the process of solvent extraction of embedding materials, such as Carbowax and paraffin, from the sections. A number of photographs are shown of the high speed microtome as well as electron micrographs of a few sections produced by the instrument. These pictures of rubber, rayon, Lucite, block Nylon, and animal tissue indicate some of the fields of application of the microtome and demonstrate the effectiveness of the necessary auxiliary techniques for it, particularly sample hardening and embedding, and section collecting and mounting.

54 citations


Journal ArticleDOI
TL;DR: A pneumatic heat detector is described in which radiant energy is dissipated in a black absorber which is located in the center of a gas cell and serves to distort a collodion film located a few thousands of an inch from a nearby parallel glass window.
Abstract: A pneumatic heat detector is described in which radiant energy is dissipated in a black absorber which is located in the center of a gas cell. The resulting heating and expansion of the gas serves to distort a collodion film located a few thousands of an inch from a nearby parallel glass window. The distortion of the film is detected by observing a shift in a system of interference fringes formed by light reflected from the film and the adjacent glass surface. The principle lends itself readily to the design of systems comprising a multiplicity of heat cells and associated detecting films. A system utilizing 61 cells is described.

41 citations


Journal ArticleDOI
TL;DR: A new interferometer is described which carried investigations to the four‐megacycle region, and preliminary measurements on H2 gave evidence of molecular dispersion between four and eight megacycles.
Abstract: A method of determining the constants of propagation for ultrasonic waves in gases, by use of the Pierce interferometer, was devised by Hubbard, and application of it extended to a limit of two megacycles by his various students. Herein is described a new interferometer which carried these investigations to the four‐megacycle region. Alignment of the piston and crystal to the order of one light fringe was attained and maintained by employing Newton and Haidinger optical fringe systems. Velocities were measured to an accuracy of one‐tenth of one percent, and absorption and reflection coefficients to fifty percent in air and CO2. The limit of accuracy in both cases was determined by the measurement of length, as measured to one micron with a micrometer screw. Preliminary measurements on H2 gave evidence of molecular dispersion between four and eight megacycles.

28 citations


Journal ArticleDOI
TL;DR: A new type of vacuum gauge is described for measuring pressures in the range between zero and 10 millimeters of mercury, actuated by the ionization current resulting from the action of the radiation from a minute amount of radium on a small portion of the atmosphere within the vacuum system.
Abstract: A new type of vacuum gauge is described for measuring pressures in the range between zero and 10 millimeters of mercury. The gauge response is a linear function of pressure. Three sensitivity ranges are provided by a selector switch giving pressure ranges of 0 to 0.1 millimeter, 0 to 1.0 millimeters, and 0 to 10 millimeters, the second value in each case corresponding to full‐scale deflection of the output meter. The gauge is actuated by the ionization current resulting from the action of the radiation from a minute amount of radium on a small portion of the atmosphere within the vacuum system.

27 citations


Journal ArticleDOI
TL;DR: This paper deals with the methods and equipment used in the construction of small high speed bolometers, particular attention is given to the Type G unit which is rugged, sensitive, and capable of being used satisfactorily with radiation modulated at 30 cycles per second.
Abstract: This paper deals with the methods and equipment used in the construction of small high speed bolometers. Particular attention is given to the Type G unit which is rugged, sensitive, and capable of being used satisfactorily with radiation modulated at 30 cycles per second. Special units can be used at considerably higher frequencies. Descriptions are given of methods and equipment for making the cellulose nitrate supporting film and for evaporating thin strips of gold onto this film. Deposition of electrodes and methods of testing for noise and sensitivity during the course of production are described. The use of metal back plates, separated from the bolometer strip by a small distance, is shown to be advantageous. With this construction, and a gas pressure of 20 mm of nitrogen, very satisfactory frequency characteristics are obtained. Gold black is used to increase the absorption of radiation in the vicinity of 10μ. It is pointed out that by controlling the gas pressure either resistive or conductive laye...

20 citations


Journal ArticleDOI
TL;DR: The statistical interpretation of the counting rate meter output readings due to the randomly distributed pulses from radioactive sources requires a special statistical theory because an integrating and averaging circuit produces an exponential interdependence of successive observations on all preceding observations.
Abstract: The counting rate meter is an electronic amplifier and computing circuit whose output is a d.c. current or voltage proportional to the number of pulses fed into the circuit. The input pulses may be either uniformly spaced or distributed randomly in time, as in the most common use of the instrument as an amplifier and recorder for use with Geiger‐Muller counters. The electronic design and operation is discussed for each of the circuit components: amplifiers, pulse equalizer, integrating circuit, degenerative vacuum‐tube voltmeter, and the stabilized high voltage and low voltage supplies. The statistical interpretation of the counting rate meter output readings due to the randomly distributed pulses from radioactive sources requires a special statistical theory because an integrating and averaging circuit produces an exponential interdependence of successive observations on all preceding observations. Practical methods, with curves, are developed for determining the mean counting rate and the probable error...

19 citations


PatentDOI
TL;DR: In this paper, a variety of proportional counter designs may be developed which are stable both with and without thin windows, and a few counter designs which have applications in the detection of alpha-radioactive contamination are discussed in detail.
Abstract: Some properties of proportional counters using air at atmospheric pressure are described. It is shown that a variety of counter designs may be developed which are stable both with and without thin windows. A few counter designs which have applications in the detection of alpha‐radioactive contamination are discussed in detail.

Journal ArticleDOI
TL;DR: 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: A simple and inexpensive degenerative electronic stabilizer which operates at ground potential in the primary a.c. line is described to maintain the current and voltage of a high wattage continuously pumped x‐ray tube constant to about 0.1 percent.
Abstract: 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.

Journal ArticleDOI
TL;DR: With sufficient amplification of the pulses from a G‐M counter, it was observed that the deadtime decreased as the counting rate increased and the maximum counting rate of a tube could be advanced to 100,000 counts per second.
Abstract: With sufficient amplification of the pulses from a G‐M counter, it was observed that the deadtime decreased as the counting rate increased. The maximum counting rate of a tube could be advanced to 100,000 counts per second although its apparent resolving power at low rates did not exceed 10,000 per second. Above 10,000 counts per second the resolving power increased almost in proportion to the counting rate.

Journal ArticleDOI
TL;DR: A simple, rugged, and reliable apparatus for the measurement of contact potential differences (in the future abbreviated CPD) by a modified Kelvin method is described.
Abstract: A simple, rugged, and reliable apparatus for the measurement of contact potential differences (in the future abbreviated CPD) by a modified Kelvin method is described. The null circuit using a 6F5 as electrometer tube has a sensitivity of 0.5‐cm scope deflection/mv of CPD/cm2 sample area, which permits the CPD to be determined to 1/100 volt for samples with surface areas as small as two square millimeters. The apparatus was developed for the study of surface characteristics of metals.


Journal ArticleDOI
TL;DR: In this article, an instrument for measurement of the magnetic properties of samples of small cross-sectional area is described, where the signal from two opposed pick-up coils, one of which contains the sample, is integrated, amplified, and applied to the vertical deflecting plates of a cathode-ray oscillograph.
Abstract: An instrument for measurement of the magnetic properties of samples of small cross‐sectional area is described. The signal from two opposed pick‐up coils, one of which contains the sample, is integrated, amplified, and applied to the vertical deflecting plates of a cathode‐ray oscillograph. Each of the pick‐up coils lies in one of a pair of identical magnetizing solenoids. The signal from a non‐inductive resistance in series with the solenoids provides the horizontal deflection for the cathode‐ray oscillograph so that the hysteresis loop of the sample is displayed on the fluorescent screen. The instrument is well suited for measurement of the magnetic properties of samples having cross‐sectional areas of the order of magnitude of 10−5 cm2.



Journal ArticleDOI
TL;DR: Three types of counters which have proved particularly useful in this laboratory are described: 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.
Abstract: Every laboratory working in the field of radioactivity, develops many types of Geiger‐Muller 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.

Journal ArticleDOI
TL;DR: In this paper, an instrument is described which is capable of measuring one part of helium in 400,000 parts of other gases and is built around a 180° type mass spectrometer tube which is prefocused for helium ions.
Abstract: An instrument is described which is capable of measuring one part of helium in 400,000 parts of other gases. The instrument is built around a 180° type mass spectrometer tube which is prefocused for helium ions. Use is made of this high sensitivity tube to locate leaks in vacuum equipment. The leaky container can be connected and evacuated by the pumps in the unit. A fine stream of helium played over the surface of the container will enter the leak and register immediately on the output meter. Very small leaks can be located easily to within a quarter of an inch. The unit is completely self‐contained, requiring only a line connection to a 110‐volt a.c. outlet.

Journal ArticleDOI
TL;DR: In this article, a direct-coupled pentode trigger pair is made the basis of two simple ring-of-ten circuits for high-speed counting, one of which is especially suited for counting sharp pulses up to a frequency of 105 cycles per second.
Abstract: A direct‐coupled pentode trigger pair, previously described, is made the basis of two simple ring‐of‐ten circuits for high speed counting. One of the circuits is especially suited for the counting of sharp pulses up to a frequency of 105 cycles per second. The other circuit is especially suited for frequency measurements on periodic currents of arbitrary wave form and of frequency from zero to above 105 cycles per second. The number of pulses or cycles counted by one ring‐of‐ten is indicated on the screen of a cathode‐ray oscilloscope tube. Several of these ring‐of‐ten units, each with its cathode‐ray tube, can be connected in cascade to make electronic counting with direct indication of the decimal figures possible.

Journal ArticleDOI
TL;DR: 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.
Abstract: A small Geiger‐Muller 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.



Journal ArticleDOI
TL;DR: A sample changer used in the routine measurement of large numbers of radioactive samples is described and circuits and methods of preparing samples are included.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, a viscometer consisting of a glass jet which is inserted in a closed system is described, and the results suggest an analytical criterion for assessing the transition from laminar to turbulent flow at high rates of shear.
Abstract: A viscometer consisting of a glass jet which is inserted in a closed system is described. With this instrument high rates of shear of the order of magnitude of 100,000 sec.−1 can be reached for hydraulic oils. Observations on straight mineral oils of sufficiently high viscosity to exclude turbulence, on refined rape oil, and on castor oil, showed that Poiseuille's law was obeyed, i.e., the rate of flow was strictly proportional to the pressure difference applied to the jet. On the other hand, for colloidal solutions temporary viscosity reductions became apparent when 1/t, the reciprocal value of the time of flow of a given volume, was plotted against p, the pressure difference, and when it was ascertained that the lowest value which the viscosity would reach was still high enough to exclude the occurrence of turbulent flow. Whenever the condition of turbulent flow applied, the curvature of the (1/t)—p curve was in the opposite direction so that in those cases in which the temporary viscosity reduction would bring the system within the range of turbulent flow a change in direction and curvature of the (1/t)—p curve would take place with the result of either indicating an asymptotic approach to a straight line or, in more pronounced cases, showing a point of inflection. For colloidal solutions the results suggest an analytical criterion for assessing the transition from laminar to turbulent flow at high rates of shear. In the laminar region log (pt) was found to decrease linearly with increasing values of the logarithm of the mean rate of shear. With the instrument described here laminar flow was found to persist when Reynolds' numbers up to about 44,000 were encountered. However, the critical Reynolds' number is not necessarily the same for the same oil and two different jets as the beginning of turbulence may depend upon the geometrical shape of the jet.

Journal ArticleDOI
TL;DR: This paper contains a survey of the characteristics and uses of non‐linear circuit elements in the generation of wave forms particularly useful in precision timing circuits.
Abstract: This paper contains a survey of the characteristics and uses of non‐linear circuit elements in the generation of wave forms particularly useful in precision timing circuits. The use of these non‐linear circuit elements in detection and time measurement is also included.

Journal ArticleDOI
TL;DR: In this paper, a simple Hampson-type liquefier capable of producing about a liter of liquid hydrogen per hour is described, without the necessity of a compressor or gasometer.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, a trigger circuit using two pentodes with direct plate-to-screen coupling is described, and the mechanism of electrical stability and instability and the process of triggering are discussed.
Abstract: A trigger circuit using two pentodes with direct plate‐to‐screen coupling is described. The mechanism of electrical stability and instability and the process of triggering are discussed. Sample diagrams for a pulse generator, an electronic switch, and a scaling circuit are given.