Showing papers in "Review of Scientific Instruments in 1955"
TL;DR: In this paper, a new type of ion gun is described which greatly improves the resolution of a nonmagnetic time-of-flight mass spectrometer, and the focusing action of this gun is discussed and analyzed mathematically.
Abstract: A new type of ion gun is described which greatly improves the resolution of a nonmagnetic time‐of‐flight mass spectrometer. The focusing action of this gun is discussed and analyzed mathematically. The validity of the analysis and the practicability of the gun are demonstrated by the spectra obtained. The spectrometer is capable of measuring the relative abundance of adjacent masses well beyond 100 amu.
3,428 citations
TL;DR: In this paper, a retarding potential difference (RPD) method was used to obtain ionization probability curves with essentially monoenergetic electrons, where the difference in the ionization produced in the two cases is ionization by those electrons with a small energy spread selected from the original distribution.
Abstract: Over the last few years, a method has been developed for obtaining ionization probability curves with essentially monoenergetic electrons. A retarding potential is applied to the electron beam to yield an energy distribution with a sharp low‐energy limit. By varying the retarding potential slightly, a new low‐energy limit of the distribution can be selected. The difference in the ionization produced in the two cases is ionization by those electrons with a small energy spread selected from the original distribution. By pulsing the electrons and ions, it is possible to eliminate the adverse effect of the ion‐drawout field on the electron energy. With this retarding potential difference (RPD) method, a detailed analysis of ionization probability curves is possible. A full description of this method is given in this paper with a discussion of its advantages and limitations. The mass spectrometer used in this series of studies is described, particular attention being given to a description of the ion source. The various electrodes of the electron beam slit system are described in terms of their influence on the electron energy, and on the shapes of ionization probability curves.
211 citations
TL;DR: In this article, the deflection of electrons in a uniform electric field can serve to measure the distribution of their energies, has been investigated both theoretically and experimentally, and an analyzer built to this design with an over-all length of five inches was able to completely separate electrons having a difference in their energies.
Abstract: The well‐known principle that the deflection of electrons in a uniform electric field can serve to measure the distribution of their energies, has been investigated both theoretically and experimentally. Simple theory suggests a particular choice of parameters for an instrument intended for such measurements. Design equations are presented, dimensions of a practical device are given, and the necessary associated electric circuits are discussed. An instrument of this type employes only an electric field, is small in size, is easily constructed, and provides a linear scale of energy values. An analyzer built to this design with an over‐all length of five inches was able to completely separate electrons having a difference in their energies of two percent.
125 citations
TL;DR: Scitation as discussed by the authors is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies (AIP member societies) from the 1990s and 2000s.
Abstract: Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
104 citations
TL;DR: In this paper, a proportional counter filled with helium-3, krypton, and carbon dioxide is irradiated with neutrons, and the spectrum can be obtained by observing the pulse height distribution.
Abstract: The neutron transformation of helium‐3 has been applied to neutron spectroscopy in the medium energy range in order to overcome the disadvantages of previous methods which have usually been based on neutron scattering. By observing the pulse‐height distribution when a proportional counter filled with helium‐3, krypton, and carbon dioxide is irradiated with neutrons, the spectrum can be obtained. Details of the counter construction and vacuum equipment for filling the counter are described. In the range of energy from thermal to 1 Mev the spread (relative standard deviation of a peak) is about 3% and the wall effect agrees with theoretical predictions. The pulse height varies linearly with energy and some evidence suggesting that the mean energy required to produce an ion pair in krypton for helium‐3 nuclei is about 6% greater than that for protons is presented. Since the neutron reaction cross section of helium‐3, as a function of energy, is required to evaluate neutron spectra from observed distributions...
91 citations
70 citations
TL;DR: In this article, the sharpness of the Curie transition depends to a large extent on the size of the BaTiO3 crystallites and the structure of the film seems to influence the dielectric constant and the saturation and remanent polarization.
Abstract: Ferroelectric films of BaTiO3 approximately 1 to 2 microns thick have been formed on platinum substrates by evaporation in a vacuum and a subsequent heat treatment in air. The structure of the crystallites which make up the films is mainly perovskite with the hexagonal phase as a minor constituent. Dielectric measurements show that the Curie temperature is about 120°C. The sharpness of the Curie transition depends to a large extent on the size of the BaTiO3 crystallites. The structure of the film seems to influence the dielectric constant and the saturation and remanent polarization of the film.
67 citations
TL;DR: In this article, a micro-calorimeter for the measurement of microwave power with relatively high accuracy (better than 1 percent) and at low (milliwatt) power levels is described.
Abstract: This paper gives a brief account of a calorimeter developed at the National Bureau of Standards for the measurement of microwave power with relatively high accuracy (better than 1 percent) and at low (milliwatt) power levels. The calorimeter is identifiable as an electrically (dc) calibrated, aneroid micro‐calorimeter of the Joule twin type. A bolometer mount assembly serves as a wave‐guide termination for the absorption of microwave power and constitutes the calorimetric body whose temperature rise is observed. This arrangement enables the use of a novel indirect measurement technique and tends to insure calorimetric equivalence of dc and rf heating. The equivalence error is investigated with the aid of heat flow analysis and auxiliary experiments, and an upper bound for the error is assigned.
66 citations
TL;DR: In this article, an apparatus for measuring resistivity and Hall coefficient of semiconductors is described using a new type of measuring circuit, which combines the best features of both ac and dc apparatus.
Abstract: An apparatus for measuring resistivity and Hall coefficient of semiconductors is described. Using a new type of measuring circuit, it combines the best features of both ac and dc apparatus. Thus, on the one hand, errors due to thermal emf's and the Ettingshausen effect are eliminated while, on the other hand, the one necessary balance is still made on a simple dc potentiometer with a dc galvanometer as null indicator. Contact and lead resistances do not affect the readings. Results of resistance and Hall coefficient measurements on a germanium specimen are given as an indication of performance.
66 citations
TL;DR: In this paper, a high resolution microwave spectrometer, which produces lines substantially narrower than the usual Doppler width, is described for exciting gases to states from which they emit coherent spontaneous radiation in the microwave frequency region.
Abstract: Methods are described for exciting gases to states from which they emit coherent spontaneous radiation in the microwave frequency region. The excitation is produced by the application of short pulses of microwave power. The power subsequently radiated by the gas is calculated for several cases, and experimental methods used to detect the radiation are described. The problem of sensitivity is discussed and compared to the sensitivity obtainable in a continuous absorption experiment. The operation of a high resolution microwave spectrometer, which produces lines substantially narrower than the usual Doppler width, is described. The method used to stabilize the klystron used in these experiments, which is a modification of the Pound i.f. method, is given.
62 citations
TL;DR: In this article, a monitor for high-energy beams of charged particles utilizing the phenomenon of secondary emission is described, where the primary beam to be monitored passes through a set of foils alternately phased in voltage.
Abstract: A monitor for high‐energy beams of charged particles utilizing the phenomenon of secondary emission is described. The primary beam to be monitored passes through a set of foils alternately phased in voltage. The current produced by secondary electrons ejected by the beam passage is collected onto the one set of foils and measured. Results of tests with high‐energy electrons are given. The monitor gives no indication of saturation up to peak current densities of 16 ma/cm2, and is independent of the primary beam energy in the range over which the monitor was tested (111–235 Mev).
TL;DR: In this article, a linear accelerator with 46 axial ''drift tubes'' was used to increase the energy of protons from a 4-Mev Van de Graaff injector to a final energy of 31.5 Mev.
Abstract: A linear accelerator is now in use which increases the energy of protons from a 4‐Mev Van de Graaff injector to a final energy of 31.5 Mev. The accelerator consists of a cavity 40 feet long and 39 inches in diameter, excited at resonance in a longitudinal electric mode with a radio‐frequency power of about 2.1×106 watts peak at 202.5 Mc. Acceleration is made possible by the introduction of 46 axial ``drift tubes'' into the cavity, which is designed so that the particles traverse the distance between the centers of successive tubes in one cycle of the rf power. The proton bunches are longitudinally stable as in the synchrotron, and are stabilized transversely by the action of converging fields produced by focusing grids. The electrical cavity is constructed like an inverted airplane fuselage and is supported in a vacuum tank. Power is supplied by 9 high‐powered oscillators fed from a pulse generator of the artificial transmission line type. Output currents are 3×10−7 ampere, average, and 60 μa, peak. The beam has a diameter of 1 cm and an angular divergence of 10−3 radian.
TL;DR: In this article, a high-sensitivity, automatic recording paramagnetic resonance absorption spectrometer operating at a wavelength of 3.2 cm is described, where automatic frequency control of the signal and localoscillator klystrons is provided to eliminate anomalous dispersion and to reduce frequency fluctuations.
Abstract: A high‐sensitivity, automatic recording paramagnetic resonance absorption spectrometer operating at a wavelength of 3.2 cm is described. The spectrometer is of the crystal‐heterodyne type employing a local‐oscillator and a magic tee bridge with a reflection cavity. Automatic frequency control of the signal and local‐oscillator klystrons is provided to eliminate anomalous dispersion and to reduce frequency fluctuations. The output signal can be presented as a trace of the paramagnetic absorption versus magnetic field on a continuous strip recorder, as a pattern on an oscilloscope of absorption versus magnetic field for either visual observation or photographic recording, or as a continuous recorder trace of the derivative of absorption versus magnetic field. Provision is made for calibration of the magnetic field by means of the proton magnetic resonance absorption. Approximately 2×10−11 mole of 1, 1‐diphenyl‐2‐picryl hydrazyl can be detected with the spectrometer.
TL;DR: In this paper, an interference filter and a gated photomultiplier were used for the study of the decay of the concentration of metastable atoms following a pulsed discharge.
Abstract: Time sampling techniques have been applied to the study of optical absorption transients. The method is described in terms of its use for the study of the decay of the concentration of metastable atoms following a pulsed discharge. Light from a capillary source is passed through the discharge tube. The transmitted intensity of one of the spectral lines which is absorbed by the metastable atoms is measured using an interference filter and a gated photomultiplier. The photomultiplier gate occurs at twice the discharge frequency so that alternate pulses of the photomultiplier output are reduced by absorption. The component of the photomultiplier output at the discharge frequency is proportional to the absorption and can be measured with a narrow band amplifier and synchronous detector. Since the time resolution of the system is determined by the width of the photomultiplier gate, the response of the synchronous detector can be made slow enough to average the absorption signal over many decay periods. Fluctuations in the number of electrons leaving the cathode of the photomultiplier limit the useful sensitivity of the present system to approximately two parts in 104. This represents a hundredfold improvement in sensitivity over that available with previous techniques. The results of some studies of helium metastables are presented in order to illustrate the detail which can be obtained with this technique.
TL;DR: In this article, the Eulerian Cradle is used for orienting single crystals in an x-ray beam, in order to bring each reciprocal lattice point into the equatorial plane for Geiger counter measurement of the intensity.
Abstract: A device for measuring x‐ray diffractions from a single crystal is described. The heart of the apparatus is an ``Eulerian Cradle,'' so named because it permits rotation of the crystal about each of the Eulerian axes. It is used for orienting single crystals in an x‐ray beam, in order to bring each reciprocal lattice point into the equatorial plane for Geiger counter measurement of the intensity. It eliminates the need for raising the Geiger tube out of the equatorial plane and suggests that the reciprocal lattice be surveyed by either ``zone'' or ``cone'' schemes. These are described, and the ``cone'' scheme is shown to permit a complete hemisphere of the reciprocal lattice to be surveyed with only a single mounting of any crystal. Fine points concerning the use of the apparatus in the precise orientation of a crystal, and for the measurement of integrated intensities at single settings, are given. All angular motions are controlled by worm wheels and worms with dials for direct reading to 0.01°. Data collection is further facilitated by computing appropriate angular coordinates for reciprocal lattice points from an accurate set of lattice parameter measurements (readily obtained with the same instrument) and setting the various circles accordingly. The long spacings, characteristic of protein crystals, require both the high precision of this instrument and computed coordinates for the many thousands of reflections that must be measured.
TL;DR: In this paper, the spectral sensitivities of such photon counters are determined by the photoelectric characteristics of the cathodes and the absorption and photoionization properties of the filling gases.
Abstract: Photosensitive Geiger counters are useful for detection of ultraviolet radiation between 1050 A and 2500 A. The spectral sensitivities of such photon counters are determined by the photoelectric characteristics of the cathodes and the absorption and photo‐ionization properties of the filling gases. Electronegative gases increase the cathode work function and greatly reduce by negative ion formation the probability that a photoelectron will initiate a count. By proper combinations of gases to fix the long wavelength limit of counter sensitivity and filters to limit the short wavelength responses, it is possible to construct relatively narrow band detectors for the extreme ultraviolet. Such tubes have been used to study the solar spectrum from rockets and have been applied in the laboratory to absorption measurements of concentrations of gases such as H2O in air and O2 in the presence of H2, N2, and the rare gases. Characteristics of solid and gaseous materials useful in vacuum ultraviolet work are listed.
TL;DR: In this paper, a time-of-flight mass spectrometer based on principles previously described has been constructed with two major modifications to facilitate appearance potential measurements, such as an axial electron beam is pulsed through an ionization chamber utilizing techniques of Fox, et al., and a gated ion detector is employed to integrate the resolved ion current from successive cycles.
Abstract: A time‐of‐flight mass spectrometer based on principles previously described has been constructed with two major modifications to facilitate appearance potential measurements. These modifications are (1) an axial electron beam is pulsed through an ionization chamber utilizing techniques of Fox, et al., and (2) a gated ion detector is employed to allow for integration of the resolved ion current from successive cycles. The instrument has been constructed of stainless steel to allow for measurements on chemically active gases. Theoretical resolution, limited by thermal energies of the ions, appears to be well over mass 200. Preliminary experimental work has verified this up to the region of mass 100. Ionization potentials, using the difference method, have been obtained from various gases that are in agreement with the spectroscopic data to within 0.05 volts.
TL;DR: In this article, a fast neutron spectrometer, using the time of flight method, which may also be used to study reactions involving the simultaneous emission of neutrons and gamma rays, is described.
Abstract: A fast neutron spectrometer, using the time of flight method, which may also be used to study reactions involving the simultaneous emission of neutrons and gamma rays, is described. One stilbene scintillation counter is placed close to the source, the other a suitable distance away. The two are connected to a new type of coincidence time sorter which converts delay time between associated events into a pulse amplitude distribution which may be analyzed by a kicksorter, so enabling the whole range of delay times or energies to be displayed and recorded at one time. The delay time may result from neutron flight time following scattering in the first counter, from the time of flight of a neutron from the target associated with a gamma ray entering the first counter, or from a charged particle associated with a gamma ray. Using D(d,n)He3 neutrons and a flight path of 50 cm, it has been possible to measure the energy with an accuracy of 10%. Angular correlations arising from (−,nγ) reactions may be studied wit...
TL;DR: In this paper, an electron-electron coincidence spectrometer is described, where magnetic lenses are used for the energy selection in each channel, and the coincidence counting efficiency is increased by using long lens spectrometers.
Abstract: An electron‐electron coincidence spectrometer is described. Magnetic lenses are used for the energy selection in each channel, and the coincidence counting efficiency is increased by using long lens spectrometers. At an effective transmission of 3%, relative half‐widths of 1.3% (source diameter 0.2 cm) and 3.1% (source diameter 0.5 cm) were obtained. ``Triangular field'' focusing, introduced here, gives a favorable high luminosity in spite of small dimensions, distance between source and detector being only 25 cm in each half of the instrument. The focusing properties of this field form are discussed. Anthracene crystals cemented onto Lucite light guides serve as detectors, and it is shown that the light transmission efficiency of the guides can be considerably improved by machining them to a certain profile theoretically corresponding to 100% light collection. In practice efficiencies of 70−60% are obtained for Lucite light guides between 10 cm and 20 cm. The performance of the instrument is illustrated by some results obtained with coincidence measurements on the electron spectrum of Pb200.
TL;DR: In this article, a breaker-type dc amplifier suitable for measurement of thermocouple voltages as low as 10−2 μvolt is described, and a temperature regulation circuit is described which is suitable for precision control of temperature.
Abstract: A breaker‐type dc amplifier suitable for measurement of thermocouple voltages as low as 10−2 μvolt is described. Mechanically driven ``choppers'' operating at 40 cps are used to modulate the thermocouple signal and later demodulate the amplifier output. Both input and output are floating and may normally be operated connected to ungrounded circuits. Over‐all voltage gain is approximately 107 while the zero error corresponds to less than 10−2‐μvolt dc input within five minutes of turning on. The amplifier contains only standard components and details of a suitable chopper which can be made in the laboratory are given.A temperature regulation circuit is described which is suitable for precision control of temperature in conjunction with a differential thermocouple. An indicated temperature match as close as 0.0002°C has been obtained with a single couple.
TL;DR: In this article, an analytical balance is described in which the materials to be weighed are attached to a ferromagnetic body that is freely suspended by the axial magnetic field of a solenoid.
Abstract: An analytical balance is described in which the materials to be weighed are attached to a ferromagnetic body that is freely suspended by the axial magnetic field of a solenoid. The vertical position of the suspended mass is maintained by the automatic regulation of the current through the solenoid by means of an electronic servo‐circuit actuated by a light beam and photomultiplier tube arrangement. The horizontal position of the supported mass is maintained by the symmetrically diverging field of the solenoid. Changes in the nonferromagnetic masses of the suspended bodies are determined by the resulting changes in the current through the solenoid necessary to keep the bodies freely suspended. Masses ranging from 105 grams to 2×10−6 gram have been suspended. The precision of the balance is limited only by the natural fluctuations in the circuit, the photomultipliers and the support system. This balance is especially useful where it is necessary to weigh materials inside of sealed chambers which contain gases, vapors or liquids, or which are evacuated. A method is described for accurately calibrating the balance.
TL;DR: The results of the investigation of three methods of obtaining transverse stability in linear accelerators for ions are presented and discussed in this paper, where the range of stable operation, oscillation amplitudes, and the effect of perturbing errors are treated.
Abstract: The results of the investigation of three methods of obtaining transverse stability in linear accelerators for ions are presented and discussed. For electric or magnetic quadrupole focusing the range of stable operation, oscillation amplitudes, and the effect of perturbing errors are treated. For grid focusing, the operation of an actual grid is analyzed from measurements of the field distribution. Finally, the formulas applicable to focusing by axial magnetic lenses are presented.
TL;DR: In this paper, various zinc sulfide phosphor mixtures for neutron scintillation counting have been compared and the low sensitivity of these mixtures to gammas (10−5−10−4 percent) and the measured short time decay constant (τ=0.04 μsec) offer distinct advantages for fast neutron counting.
Abstract: Various zinc sulfide phosphor mixtures for neutron scintillation counting have been compared. Selected compounds of hydrogen, lithium, boron, and fissionable elements were mixed in varying proportions with ZnS(Ag), and the corresponding neutron and gamma counting efficiencies measured as functions of energy. The low sensitivity of these mixtures to gammas (10−5−10−4 percent) and the measured short time decay constant (τ=0.04 μsec) offer distinct advantages for fast neutron counting.
TL;DR: In this article, the decay times of a number of organic crystal, liquid, and plastic scintillators are reported, excited by pulses of x-radiation of 7.5-kev quantum energy.
Abstract: The luminescence decay times of a number of organic crystal, liquid, and plastic scintillators are reported. The scintillators were excited by pulses of x‐radiation of 7.5‐kev quantum energy. The dimensions of the specimens are given, although the effect of specimen size on decay time was not investigated.
TL;DR: In this article, a torsional magnetic susceptibility balance suitable for studying the de Haas van Alphen effect has been developed in which the torque and magnetic field are recorded continuously while the magnet current is reduced automatically.
Abstract: A torsional magnetic susceptibility balance suitable for studying the de Haas‐van Alphen effect has been developed in which the torque and magnetic field are recorded continuously while the magnet current is reduced automatically. The torque is recorded as a bucking current to a galvanometer suspension supporting the sample, and the magnetic field is obtained from a recording of the magnet current. A circuit for stabilizing the magnet current is also described.
TL;DR: In this paper, a simple system for determining the velocity of detonation or strong shock waves, with temperatures above 3000°K, by using the conductivity behind the wave was described.
Abstract: A simple system is described for determining the velocity of detonation or strong shock waves, with temperatures above 3000°K, by using the conductivity behind the wave. Wave contact is made by two 36‐mil wires set 0.1 inch apart in a Teflon plug mounted in the experimental tube. When a wave passes, signals are produced across a 30‐K resistor in series with these wires and a 0.001 μf capacitor charged to 300 v. Any number of circuits may be paralleled across a single signal resistor if a diode is added to each circuit to prevent signal deterioration. The arrival time of a wave at a pin can be determined with an accuracy of almost 10−8 sec from an oscilloscope record of the signals. The principal advantages of this system are excellent space resolution and very simple basic circuitry. An amplifier is described which can be used with an individual pin circuit to fire a thyratron and extend the range of applicability of this system to waves with temperatures as low as 1000°K.
TL;DR: In this paper, high sensitivity photoconductor ''powder'' layers and ''sintered'' layers have been prepared in large-area form, with most of the desirable characteristics of single crystals.
Abstract: High‐sensitivity photoconductor ``powder'' layers and ``sintered'' layers have been prepared in large‐area form, with most of the desirable characteristics of single crystals. The methods involved in the preparation of these layers are simple and avoid the difficulties involved in growing large‐area single crystals, or in producing large‐area photoconductors by evaporation in vacuum. Both types of layers can be made into photocells of any desired area, by providing suitable electrodes. At an illumination of 1 ft‐c, ratios of photo‐current to dark current as large as 106 may be obtained for both types of layers. A two‐inch square cell made from either a powder or a sintered layer can pass an ampere for an illumination of a few foot candles. In addition to their ease of fabrication, the new layers also have advantages in the large increase in red sensitivity obtainable with cadmium sulfide, and in the ohmic character of sintered layers with silver‐paste electrodes.
TL;DR: In this paper, an absolute manometer is described which provides a means of measuring vapor pressures in the range 0.5 to 20 microns with a precision and accuracy of better than one percent.
Abstract: An absolute manometer is described which provides a means of measuring vapor pressures in the range 0.5 to 20 microns with a precision and accuracy of better than one percent. Construction and use of the manometer is described in detail and an analysis of the possible sources of error is given. The vapor pressure of mercury has been determined and is presented to give an example of the performance of the manometer.
TL;DR: In this paper, a graph of the calculated percentage transmission of the windows is presented, and the calculated quantum counting efficiencies for the range 0.1 to 15 A are shown for an end-window argon-filled Geiger counter, side-window Xe, Kr, A, and Ne proportional counters and an NaI·Tl scintillation counter.
Abstract: Mass absorption coefficient data published by Allen, Bragg, and Victoreen for the wavelength region 0.1 to 50 A are plotted for several common x‐ray tube and counter windows (Al, Be, and mica) and gases (Xe, Kr, A, and Ne) used in x‐ray detectors. A graph of the calculated percentage transmission of the windows is presented. The calculated quantum‐counting efficiencies for the range 0.1 to 15 A are shown for an end‐window argon‐filled Geiger counter, side‐window Xe, Kr, A, and Ne proportional counters and an NaI·Tl scintillation counter. Some of the factors to be considered in the choice of detectors for x‐ray diffractometry and x‐ray spectroscopy are discussed particularly with respect to the spectral sensitivity.