Showing papers in "Review of Scientific Instruments in 1954"
TL;DR: In this paper, a double-beam recording spectrophotometer was developed for rapidly obtaining spectra of labile intermediates in biochemical reactions, where light from a monochromator is split into two beams by a chopping mirror and then the ratio of light intensities in two optical paths is measured.
Abstract: A double‐beam recording spectrophotometer has been developed for rapidly obtaining spectra of labile intermediates in biochemical reactions. Light from a monochromator is split into two beams by a chopping mirror and then the ratio of light intensities in two optical paths is measured. This ratio is expressed as percent absorption or converted electronically into units of optical density. Results are recorded on a linear wavelength scale at a maximum rate of 6 mμ per second. A servo system corrects the nonlinearity of the wavelength scale of the quartz monochromator. The noise level corresponds to a change of optical density of 10−4 at 400 mμ with a spectral interval of 3 mμ. The over‐all accuracy on standard solutions (National Bureau of Standards) is about 2 percent. The air‐against‐air zero absorption line varies only 0.004 in optical density from 210 to 650 mμ.
152 citations
TL;DR: Some formulas for the calculation of the solid angle subtended by a circular aperture at an isotropically emitting point or spread source as well as three tables of solid angle values are presented in this article.
Abstract: Some formulas for the calculation of the solid angle subtended by a circular aperture at an isotropically emitting point or spread source are presented as well as three tables of solid‐angle values.
118 citations
TL;DR: In this article, an interferometer of the amplitude splitting type has been constructed which operates with electron beams and produces a system of fringes in the viewing instrument, the appearance of the fringes may be varied at will by introducing changes in one of the optical paths.
Abstract: An interferometer of the amplitude‐splitting type has been constructed which operates with electron beams and produces a system of fringes in the viewing instrument. The appearance of the fringes may be varied at will by introducing changes in one of the (electron) optical paths. The instrument utilizes crystalline diffraction for beam splitting and recombining.
114 citations
TL;DR: The characteristics of a dc quadrupole magnet have been measured using some of the techniques for measuring two-dimensional fields and gradients proposed by W. C. Elmore and M. W. Garrett as discussed by the authors.
Abstract: The characteristics of a dc quadrupole magnet 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.
104 citations
80 citations
TL;DR: In this paper, fine commercial copper wire, attached with Formel varnish to a copper base, has sufficiently stable and reproducible resistance temperature characteristics to be used as a resistance thermometer in the temperature range 20°-320°K.
Abstract: Fine commercial copper wire, attached with Formel varnish to a copper base, has sufficiently stable and reproducible resistance temperature characteristics to be used as a resistance thermometer in the temperature range 20°–320°K. Excellent thermal contact is achieved by this construction; hence, unusually large heat inputs to the thermometer can be tolerated. Resistance and temperature coefficient of resistance are tabulated and limitations of accuracy discussed.
68 citations
TL;DR: In this article, the authors describe x-ray spectrometers that operate on the principle of totally absorbing the energy of an individual xray photon in a scintillator and show that detection efficiencies better than 80 percent and energy resolutions better than 10 percent are attainable in the xray energy range from ½ to 50 Mev.
Abstract: X‐ray spectrometers are described that operate on the principle of totally absorbing the energy of an individual x‐ray photon in a scintillator. Experiments with scintillators of xylene containing terphenyl, and of sodium iodide activated by thallium, show that detection efficiencies better than 80 percent and energy resolutions better than 10 percent are attainable in the x‐ray energy range from ½ to 50 Mev. Monte Carlo calculations and crude scaling laws that simplify extrapolations to other size scintillators are discussed.
54 citations
TL;DR: In this paper, a magnetic torque measuring device has been devised and tested for a cylindrical shaft under pure torsion, where the principal stress lines are 45° helices around the axis, one for tension and the other for compression.
Abstract: In a cylindrical shaft under pure torsion the principal stress lines are 45° helices around the axis, one for tension and the other for compression. These are also the directions of maximum and opposite permeability changes for a shaft of magnetostrictive material. Based on these ideas a magnetic torque measuring device has been devised and tested. It consists of an external magnetic yoke carrying a driving coil and pickup coils on each of several branches to detect the permeability changes in flux paths lying in or near the principal stress directions in the shaft. Linear response, good sensitivity and fair stability have been obtained with rotating shafts.
48 citations
TL;DR: A cylindrical liquid scintillation counter, 75 cm in diameter and 75 cm high, has been used for the detection of neutrons, gamma rays, and cosmic ray μ mesons as mentioned in this paper.
Abstract: A cylindrical liquid scintillation counter, 75 cm in diameter and 75 cm high has been used for the detection of neutrons, gamma rays, and cosmic ray μ mesons. A delayed coincidence technique has been used to detect neutrons; the first pulse corresponding to a recoil proton or other associated event, the second pulse due to neutron capture in cadmium. The capture rate of neutrons in a solution containing toluene and cadmium has been calculated as a function of the cadmium to hydrogen ration by the Monte Carlo method and an experimental check performed. Detector design considerations and some possible uses are described.
46 citations
TL;DR: In this article, two cryostats for use on very different problems which make use of this principle are described, one was used to maintain temperatures between 4° and 80°K in an application with very high heat influxes, and the second was used both to condense a liquid hydrogen cyclotron target and to maintain the target at temperatures near 20°K.
Abstract: The cooling of apparatus using liquid helium can be made a much more efficient process if the total heat content of the evaporating gas is used in addition to the latent heat of vaporization of the liquid. Two cryostats for use on very different problems which make use of this principle are described. The first cryostat was used to maintain temperatures between 4° and 80°K in an application with very high heat influxes. The second cryostat, made necessary by restrictions on the manufacture of liquid hydrogen, used liquid helium both to condense a liquid hydrogen cyclotron target, and to maintain the target at temperatures near 20°K.
46 citations
TL;DR: In this paper, the problems involved in the construction of a magnetic refrigerator operating below 1°K, using superconducting metallic links for the thermal valves and a paramagnetic salt as the working substance, are discussed.
Abstract: The problems involved in the construction of a magnetic refrigerator operating below 1°K, using superconducting metallic links for the thermal valves and a paramagnetic salt as the working substance, are discussed. A cycle for the operation of the refrigerator is suggested and then examined for the optimum operating conditions with readily available laboratory facilities. Design equations are obtained and compared with our more recent experimental model. The constructional details of a completely automatic experimental model of the magnetic refrigerator using lead for the thermal valves, iron ammonium alum as the working substance, a helium bath at 1°K as the high‐temperature reservoir, a maximum magnetic field of 7000 gauss, a 2 minute cycle of operation, and capable of extracting 120 ergs/second from a reservoir at 0.3°K are presented in full. Temperatures as low as 0.2°K are obtained with this model. Improvements in this this design, its use either for the production of an isothermal reservoir or as a heat sink for adiabatic demagnetization work below 1°K, and the extension to a two‐engine refrigerator for the production of a reservoir at temperatures as low as 0.05°K are also discussed.
TL;DR: In this paper, the electronic photometer of a recording spectrophotometer is described in detail and a segmented diode circuit is described for converting data in absorption to units of optical density with an accuracy of better than 1 percent.
Abstract: The electronic photometer of a recording spectrophotometer is described in detail. Sources of error of the circuit and experimental measurements of the inherent noise of the system are discussed. A segmented diode circuit is described for converting data in absorption to units of optical density with an accuracy of better than 1 percent. The electronic circuit of the servo system to correct the nonlinearity of the wavelength scale is also described.
TL;DR: In this article, an analytical balance has been modified by adding a solenoid and magnet so that changes in weight can be balanced electrically, and the operation is made automatic by reflecting a beam of light from the balance beam into a dual phototube in a bridge circuit and amplifying the output of the bridge to provide current in the solanoid.
Abstract: An analytical balance has been modified by adding a solenoid and magnet so that changes in weight can be balanced electrically. The operation is made automatic by reflecting a beam of light from the balance beam into a dual phototube in a bridge circuit and amplifying the output of the bridge to provide current in the solenoid. Recording the voltage drop across a resistor in series with the solenoid gives a linear weight scale which can be made to read directly in milligrams. An electronic damping circuit enables the balance to follow very rapid changes in weight without oscillating and with an accuracy better than 0.5 percent of full scale for ranges of 100 mg and over.
TL;DR: A pneumatic and an electronic regulator for helium bath temperature regulation is described in this paper, where the controller uses a carbon resistor for the thermometer and a heater inside the bath for the control element.
Abstract: A pneumatic and an electronic regulator for helium bath temperature are described. The pneumatic regulator, an automatic pressure regulating valve with large throughput, gives a simple controller suitable for regulation to a millidegree for temperatures above 1.4°K. The electronic control uses a carbon resistor for the thermometer and a heater inside the bath for the control element. Its regulation is an order of magnitude better, and it is usable at all achievable temperatures. Its theoretical analysis, circuit diagram, construction and operating details, and performance are described. Included are some general remarks and results concerning temperature regulation in He‐I and at the lambda point.
TL;DR: An electron diffraction unit incorporating a rotating sector has been developed in this paper, which makes possible the accurate and objective measurement of the intensity of electrons diffracted by free atoms and molecules.
Abstract: An electron‐diffraction unit incorporating a rotating sector has been developed which makes possible the accurate and objective measurement of the intensity of electrons diffracted by free atoms and molecules. The diffraction data afforded are sufficiently precise to permit the calculation of the distribution of electrons in atoms and the amplitude of vibration of atoms in molecules, as well as interatomic distances that are comparable in accuracy in suitable cases to those obtained by microwave spectroscopy. A description of the essential components of the unit is given together with some data on performance and discussion of the use of the apparatus.
TL;DR: In this paper, the construction of a specimen holder and furnace for use as an auxilary piece of equipment with a North American Phillips Company high angle goniometer is described, and the apparatus can be used for obtaining x-ray diffraction patterns at temperatures up to 1600°C, and at pressures in the range of 2×10−6 to 3 ×10−5 mm of mercury.
Abstract: The construction of a specimen holder and furnace for use as an auxilary piece of equipment with a North American Phillips Company high angle goniometer is described. The apparatus can be used for obtaining x‐ray diffraction patterns at temperatures up to 1600°C, and at pressures in the range of 2×10−6 to 3×10−5 mm of mercury.
TL;DR: In this paper, it has been shown that indium glass or indium-quartz bond can be soldered to thin metal films without damaging the film and giving better adhesion to the substrate.
Abstract: In the past, soldering to thin metal films on glass or quartz substrates has normally been accomplished by suitably reinforcing the film at the soldering point with a thicker underlying film This performance is necessary in order to prevent tin‐lead solders and commonly used fluxes from destroying the film and to give better adhesion to the substrate It has been found that by using the metal indium and certain of its alloys as a solder, without a flux, adherence to thin metal films may be readily obtained without destruction of the film Since indium also adheres to glass, quartz, ceramics, and silicious minerals, the strength of the joint is not determined by the strength or adherence of the metal film but by the strength of the indium‐glass or indium‐quartz bond Thus, films of only a few angstroms in thickness may be soldered without damage, with good mechanical strength and electrical contact The strength of the bond is usually about 500 pounds per square inch This technique has been found most useful in studying the resistivities of thin metal films and in the mounting of metal‐coated piezoelectric crystals Soldered connections have been made to films of 18 metals including aluminum, titanium, and zirconium
TL;DR: In this paper, two ion sources have been developed for the production of milliamperes of N+, N2+, N3+, and N4+ ions under good operating conditions, 28 ma of N3+ and 10 ma of n4+ are produced.
Abstract: Two ion sources have been developed for the production of milliamperes of N+, N2+, N3+, and N4+ ions. Under good operating conditions, 28 ma of N3+ and 10 ma of N4+ are produced. Details of source construction are given and a method for analyzing the source output is presented. Characteristics of both sources as a function of arc current and arc voltage are investigated.
TL;DR: In this paper, a fast neutron scintillator adapted to end-window photomultipliers is described for neutron detection above ∼ 0.3mV energy, achieving a detection efficiency of 3.8 percent for 4.1mV neutrons.
Abstract: A fast neutron scintillator adapted to end‐window photomultipliers is described for neutron detection above ∼0.3‐Mev energy. Light pulses are produced by the action of recoil protons from paraffine on zinc sulfide phosphor, the optimum weight ratio of the paraffine‐zinc sulfide mixture being 3:2. Interfering gamma‐ray pulses are suppressed by a 3 microsecond time‐constant in the photomultiplier output circuit, and subsequent amplitude discrimination. A detection efficiency of 3.8 percent is attained for 4.1‐Mev neutrons through the incorporation of ½‐inch deep Lucite light guides.
TL;DR: In this paper, the mechanical design features and operating characteristics of a hot-cathode arc-discharge type ion source are described, and a maximum current of 3 milliamperes of 22-Mev protons has been obtained with the source installed in the ORNL 86-inch cyclotron.
Abstract: The mechanical design features and operating characteristics of a hot‐cathode arc‐discharge type ion source are described. Proton currents of 500 milliamperes have been obtained under dc test conditions. A maximum current of 3 milliamperes of 22‐Mev protons has been obtained with the source installed in the ORNL 86‐inch cyclotron. Distinguishing features of the ion source are its arc chamber of carbon, its heavy tantalum filament heated with dc, and its use of a specially shaped accelerating electrode.
TL;DR: In this paper, a double focusing mass spectrograph for the analysis of low concentrations of impurities in solids has been developed, which is designed for either photographic or electrical ion detection.
Abstract: A double‐focusing mass spectrograph for the analysis of low concentrations of impurities in solids has been developed. The instrument is of the Mattauch type and is designed for either photographic or electrical ion detection. The construction and performance of the instrument are discussed. Bulk concentrations below 0.1 part per million, and surface contaminants of less than 0.1 monolayer, can be detected in short exposures using a photographic plate.
TL;DR: In this article, the fraction of the charged particles traversing an absorber in a counter experiment which miss the last counter because of multiple Coulomb scattering in the absorber has been calculated for a general counter geometry.
Abstract: The fraction of the charged particles traversing an absorber in a counter experiment which miss the last counter because of multiple Coulomb scattering in the absorber has been calculated for a general counter geometry. The results are presented in the form of graphs which give the fraction of surviving particles as a function of the counter geometry and the amount of multiple scattering in the absorber. It is shown that the effect of single scattering at large angles is very small.
TL;DR: A precision grinding machine was constructed to permit the study of diffusion in germanium as mentioned in this paper, which is useful for problems involving very small diffusion coefficients and radioactive tracers of very short half-life.
Abstract: A precision grinding machine was constructed to permit the study of diffusion in germanium. Because one may obtain data after mean penetrations of the order of 10μ, this instrument is useful for problems involving very small diffusion coefficients and radioactive tracers of very short half‐life. It has been found that diffusion in ductile metals such as silver may be investigated by use of this technique.
TL;DR: In this paper, a cylindrical capacitance sensor is used to measure, indicate, record, and control the level of liquefied gases inside a closed vessel, and an accuracy of ± 1.0 percent has been obtained.
Abstract: The instrument described here is designed to measure, indicate, record, and control the level of liquefied gases inside a closed vessel. It is especially designed for use at low temperatures with liquefied gases such as nitrogen, oxygen, hydrogen, and helium. It operates on a capacitance principle, and makes use of the difference in dielectric constants of the liquid and vapor. The sensing element is a cylindrical capacitor whose capacitance is a function of the height of the liquid column. The sensing capacitor is one element of an automatically balanced bridge which both indicates and records the liquid level. An over‐all accuracy of ±1.0 percent has been obtained. The sensitivity is adequate for use where the difference in dielectric constants of the liquid and vapor is 0.05 or greater. The instrument also incorporates a control function and supplies a controlled air pressure to a pneumatically operated valve for maintaining the level at a predetermined point.
TL;DR: In this paper, 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 and a sample of the frequency distribution of energy losses in each of n identical proportional counters is obtained.
Abstract: 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.
TL;DR: In this paper, a parallel plate chamber with electrode separation variable from 2 mm to 2 cm was used to measure recombination, attachment, and energy resolution for beta-ray ionization in liquid argon.
Abstract: A parallel‐plate chamber with electrode separation variable from 2 mm to 2 cm has been used to measure recombination, attachment, and energy resolution for beta‐ray ionization in liquid argon. A collecting voltage up to 30 kv was used without introducing spurious pulses. Amplifier noise sets the lower limit to beta‐ray detection at about 150 kev and limits the energy resolution to about 100 kev (full width at half maximum at any energy).
TL;DR: In this paper, a flowmeter system is described which gives continuous readings of flow velocity, with a fast rate of response, by measuring the phase difference between an upstream and downstream ultrasonic wave of, say, 100 000 cycles.
Abstract: A flowmeter system is described which gives continuous readings of flow velocity, with a fast rate of response. The ``upstream‐downstream'' method is used in which velocity of a fluid is determined by measuring the phase difference between an upstream and downstream ultrasonic wave of, say, 100 000 cycles. The functions of the transmitting and receiving transducers are interchanged at a fast rate, say 100 cycles per second, allowing the use of a synchronous rectifier. In this way, no long time stability of the phasemeter is required so that very small flow rates can be measured. Velocities as low as 0.1 cm/sec were successfully measured. A special commutator switch with very low transfer capacitance and, as an alternative, an electronic switch are described. The transducers used are barium titanate crystals mounted in a manner so that their contact with the fluid is avoided.
TL;DR: In this paper, 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.
Abstract: 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.
TL;DR: In this article, design considerations for a video microwave spectrograph using Stark modulation and a crystal or bolometer detector are presented, and a detailed description of some of the equipment in use in their laboratory is given.
Abstract: Design considerations are presented for a video microwave spectrograph using Stark modulation and a crystal or bolometer detector. Crystal and source noise is explicitly included in the treatment. A detailed description of some of the equipment in use in our laboratory is given. Some of the advantages and dis‐advantages of other systems are mentioned.