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Dec 1955

Volume 26, Issue 12, pp. 1097-1210

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Magnetic Analysis of Scattered Particles

H. P. Furth

Rev. Sci. Instrum. 26, 1097 (1955); http://dx.doi.org/10.1063/1.1715197 (4 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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The theory of conditioned probabilities is applied to the problem of momentum, charge, and mass determination from Coulomb scattered tracks in a magnetic field. An optimum procedure is derived, which makes use of both random and systematic track curvature.
It is shown that application of this procedure to a highly relativistic nuclear emulsion track of 1‐cm length in a field of 300 000 gauss will yield the momentum information of a 9.2‐cm track in zero field. If the scattering information were neglected, the effective length of the track would be 8.2 cm. At 100 000 gauss, the improvement in effective track length due to the inclusion of scattering information is shown to be by a factor of 2.3.

Ionization in a Mass Spectrometer by Monoenergetic Electrons

R. E. Fox, W. M. Hickam, D. J. Grove, and T. Kjeldaas

Rev. Sci. Instrum. 26, 1101 (1955); http://dx.doi.org/10.1063/1.1715198 (7 pages) | Cited 158 times

Online Publication Date: 29 December 2004

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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.

Null Reading Flip‐Coil Fluxmeter

H. R. Fechter and Sylvan Rubin

Rev. Sci. Instrum. 26, 1108 (1955); http://dx.doi.org/10.1063/1.1715199 (4 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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Two flip coils are rotated through 180° to give a precision measurement of the ratio of separate magnetic fields. The output voltages are connected in opposition and balanced in a resistance potentiometer using a sensitive galvanometer as a null indicator. The ratio of the fields is a linear function of the potentiometer setting. In fields of several thousand gauss and using a common shaft for the coils, readings were reproducible to within 0.01%. With separate selsyn motor drives the precision was 0.02%.

Focusing Atomic Beam Apparatus

Aaron Lemonick, Francis M. Pipkin, and Donald R. Hamilton

Rev. Sci. Instrum. 26, 1112 (1955); http://dx.doi.org/10.1063/1.1715200 (8 pages) | Cited 30 times

Online Publication Date: 29 December 2004

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The construction and design principles of a focusing atomic beam apparatus are reported. This apparatus, which is of the radio‐frequency magnetic resonance type and which has been used to measure the spins and hyperfine splittings of four radioactive nuclides as reported elsewhere, utilizes the six‐pole focusing magnet of Friedburg and Paul and of Korsunskii and Fogel but in a way which avoids velocity aberrations. From an analysis of the optimization of intensities in the conventional and the focusing types of atomic beam apparatus it is concluded that the latter has an advantage of a factor of roughly twenty‐five.

Cathode‐Ray Oscilloscope Intensity Modulator

Robert F. Kemp

Rev. Sci. Instrum. 26, 1120 (1955); http://dx.doi.org/10.1063/1.1715201 (2 pages) | Cited 2 times

Online Publication Date: 29 December 2004

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An electronic system is described for modulating the beam intensity of a cathode‐ray oscilloscope in such a manner as to reduce variations in trace brightness due to differences in writing speed. A voltage derived by a push‐pull differentiating amplifier from the vertical deflection signal is added to the instrument's intensity‐control voltage. By use of this system, improved photographs of wave forms can be obtained.

Simple Ultraviolet Radiometer

Sidney C. Stern and Charles W. Hill

Rev. Sci. Instrum. 26, 1122 (1955); http://dx.doi.org/10.1063/1.1715202 (3 pages)

Online Publication Date: 29 December 2004

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This paper describes in some detail a radiometer for measurement of ultraviolet radiation from sun and sky. As designed, the instrument is selectively responsive to a narrow band of wavelengths and is capable of detecting and measuring low‐energy levels. The radiometer consists of a photoelectric sensing element, an ultraviolet transmitting window, and a dry‐cell battery mounted in a small housing. Calibration of the instrument shows satisfactory agreement with Lambert's cosine law and a linear relationship between energy flux and output of the phototube. For recording the signal from the radiometer the output is fed to a direct current amplifier which in turn drives a recorder. A typical recording for a cloudy day is presented.

Rotary Device for Producing a Stream of Uniform Drops

A. C. Rayner and Wm. Haliburton

Rev. Sci. Instrum. 26, 1124 (1955); http://dx.doi.org/10.1063/1.1715203 (4 pages) | Cited 6 times

Online Publication Date: 29 December 2004

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A rotary device was developed to produce uniform drops of liquids in the diameter range of 50 to 700 microns. A horizontally rotating blade detaches drops in a steady stream of regular trajectory, from a stabilized liquid mass fed under constant head through a stationary capillary. Its operation is described, and performance characteristics with oil and aqueous test solutions are given. Drop size is calculated from the mass of drops emitted in a given interval at a known generation frequency. Variation in size of individual drops, electrostatic effects, and some uses for the machine are noted.

Absolute Measurement of Cyclotron Beam Currents for Radiation‐Chemical Studies

Robert H. Schuler and Augustine O. Allen

Rev. Sci. Instrum. 26, 1128 (1955); http://dx.doi.org/10.1063/1.1715204 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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Characteristics are described for the collection of cyclotron beams in a conducting medium separated from the accelerator by an insulating window. The measured current can be interpreted in terms of an absolute beam current if charge displacement within the insulator is taken into account. Collection of the beam in this manner is particularly advantageous in a region external to the cyclotron magnetic field where stray currents due to air ionization and secondary electron emission are pronounced. A comparison is made between particle energies determined by the charge‐input method and by calorimetry. A simplified arrangement for particle range determination is described.

Metal Gaskets for Demountable Vacuum Systems

P. J. Van Heerden

Rev. Sci. Instrum. 26, 1130 (1955); http://dx.doi.org/10.1063/1.1715205 (2 pages) | Cited 5 times

Online Publication Date: 29 December 2004

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Two different constructions were investigated of copper gasket seals for a demountable vacuum system. These were 5☒ inches in diameter and with both a leak rate lower than 10−6 μl∕sec could be obtained.

Precision Seconds Pulse Timing System

R. Dean Taylor and John E. Kilpatrick

Rev. Sci. Instrum. 26, 1132 (1955); http://dx.doi.org/10.1063/1.1715206 (2 pages) | Cited 6 times

Online Publication Date: 29 December 2004

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A timing system is described which provides sharp, one‐millisecond, electric pulses at one‐second intervals. These pulses are used to actuate a trigger circuit which is used to control one or more relays. The accuracy of the time scale can easily be checked against radio station WWV. Auxiliary apparatus can be controlled for time intervals of any even number of seconds. The accuracy of this interval can be determined to better than one millisecond. This system has proved to be particularly useful in calorimetry.

Improved Alpha Air Proportional Counter

Frank J. Lynch and James B. Baumgardner

Rev. Sci. Instrum. 26, 1134 (1955); http://dx.doi.org/10.1063/1.1715207 (4 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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The limitations of alpha counters using air in the proportional amplification region were investigated with a view toward a better design that would provide improved performance and reliability. A new detector is described which incorporates a shielded guard‐ring insulator assembly that provides freedom from insulator failure at high humidities. It is believed that spurious pulses also arise from the effect of humidity on the conductivity of foreign particles adhering to the anode wires. Reducing the relative humidity (rh) by the use of a small heater which maintains the detector 20°F above room temperature prevents this type of failure and provides reliable operation at 98% rh. The associated amplifier and discriminator were designed to detect the slow components of the ionization pulses associated with the transit time of negative oxygen ions. The resulting efficiency is 39% of the total disintegrations, with a plateau of over 150 volts having a slope of less than 4% per 100 volts.

C14 Dating with a Methane Proportional Counter

W. H. Burke and W. G. Meinschein

Rev. Sci. Instrum. 26, 1137 (1955); http://dx.doi.org/10.1063/1.1715208 (4 pages) | Cited 5 times

Online Publication Date: 29 December 2004

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Apparatus and procedures for conversion of sample carbon to carbon dioxide, quantitative hydrogenation of carbon dioxide to methane, and radiocarbon assay of the methane are described. Two sizes of counters are used. At the operating pressure of two atmospheres, the larger size contains 0.85 g of carbon and the smaller 0.22 g. If the sample and background are both counted for 24 hours in a 0.85‐g counter, a sample 34 000 years old (26 000 years old in the 0.22‐g counter) gives a C14 count equal to twice its standard statistical error. If desired, this method can readily be adapted to larger samples with a consequent increase in the maximum measurable age.

Third‐Order Aberration and Focusing with Sector‐Shaped Magnetic Fields

Daniel F. Dempsey

Rev. Sci. Instrum. 26, 1141 (1955); http://dx.doi.org/10.1063/1.1715209 (5 pages) | Cited 2 times

Online Publication Date: 29 December 2004

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A divergent beam of monoenergetic charged particles can be refocused by a homogeneous magnetic field whose sharply defined boundaries are straight lines or circles. The transverse aberration of order α3 at the image point is evaluated and a general third‐order focusing condition is given. Design equations for third‐order instruments are obtained and the results presented graphically. Many third‐order focusing designs follow, both symmetrical and asymmetrical.

Integrator‐Type dc Amplifier

A. J. Gardiner and H. L. Johnson

Rev. Sci. Instrum. 26, 1145 (1955); http://dx.doi.org/10.1063/1.1715210 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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A dc amplifier that uses the condenser‐charging principle of electron counting has been constructed and used for the measurement of stars as faint as magnitude 20.8 with the 82‐inch and 100‐inch telescope. The device is simple (15 tubes), will measure stars of any brightness permitted by the photomultiplier, and has a simple automatic recording feature using a Brown recording meter.

New Method for the Observation of Hyperfine Structure of NH3 in a ``Maser'' Oscillator

Koichi Shimoda and T. C. Wang

Rev. Sci. Instrum. 26, 1148 (1955); http://dx.doi.org/10.1063/1.1715211 (2 pages) | Cited 4 times

Online Publication Date: 29 December 2004

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Weak hyperfine satellites have been observed with very large signal‐to‐noise ratios when microwave power at frequencies corresponding to these satellites is introduced into a ``maser'' which is oscillating at the frequency of the main inversion line of NH3. The satellite transitions are accompanied by a reduction of the amplitude of oscillation at the main‐line frequency. A composite oscilloscope trace showing the structure of the weakest of the four quadrupole satellites associated with the 3–3 inversion line of N14H3 is presented.

Time‐of‐Flight Mass Spectrometer with Improved Resolution

W. C. Wiley and I. H. McLaren

Rev. Sci. Instrum. 26, 1150 (1955); http://dx.doi.org/10.1063/1.1715212 (8 pages) | Cited 686 times

Online Publication Date: 29 December 2004

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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.

Gas Scattering in a Strong Focusing Electron Synchrotron

Michael J. Moravcsik and J. Michael Sellen

Rev. Sci. Instrum. 26, 1158 (1955); http://dx.doi.org/10.1063/1.1715213 (7 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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Scattering of the electron beam by the residual gas in the vacuum chamber is calculated for the 1 Bev strong focusing Cornell Mesotron. It is shown that the elastic scattering by the nucleus and the inelastic scattering by the atomic electrons are the only important contributions to the loss due to the presence of gas. These two effects are calculated in detail. Radiation and space charge effects are not discussed. Because of the small scattering angles involved the details of the screening by the atomic electrons must be taken into account accurately. Multiple scattering is shown to be of little importance because of the damping of the beam oscillations as the energy increases. The calculations are carried out for two different injection conditions and little difference is found between them as far as the loss due to the scattering itself is concerned. The numerical results for the Cornell Mesotron show that about half of the beam gets lost at a vacuum of 5×10−6 mm Hg. The scattering losses will depend on the field lattice of the synchrotron.

Fast Neutron Coincidence Spectrometer. II

Paul R. Chagnon, George E. Owen, and Leon Madansky

Rev. Sci. Instrum. 26, 1165 (1955); http://dx.doi.org/10.1063/1.1715214 (6 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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A fast neutron coincidence spectrometer utilizing stilbene scintillators is described. The principle of the spectrometer is based upon the pulse‐height analysis of the recoil protons resulting from a 45 degree scattering of the incident neutron beam. This is achieved by requiring the scattered neutron to be recorded in a secondary ring of ten stilbene scintillators. With delays corresponding to a fixed time of flight, a coincidence between the primary and secondary crystals gates the primary pulse. At 4 Mev the efficiency is of the order of 10−4 per incident neutron, and the pulse‐height distribution has a width at half‐maximum of 17%. The corresponding energy width is 10%. The time‐of‐flight characteristic is used to reject gamma rays. Limitations caused by accidentals and pulse‐height resolution are discussed.

Three‐Terminal Dielectric Cell with a Floating Micrometer Electrode

Richard N. Work

Rev. Sci. Instrum. 26, 1171 (1955); http://dx.doi.org/10.1063/1.1715215 (5 pages) | Cited 6 times

Online Publication Date: 29 December 2004

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A description is given of a three‐terminal cell for dielectric measurements on polymeric materials over a wide temperature range. Use is made of a lightly spring‐loaded, floating electrode to maintain good electrical contact with the specimen when it expands or contracts thermally. A differential‐capacitor, built into the movable electrode, is used with a simple detector circuit to indicate the position of the electrode with respect to its micrometer‐driven carriage. Simultaneous measurements can be made of cell capacitance and electrode separation. The latter can be determined with a precision of better than 10−4 inch. Provision is made to confine the specimen when it softens at temperatures above its glass‐transition temperature. The cell has been operated successfully at frequencies between 20 cps and 1 Mc and at temperatures between 20 and 200°C.

Electronic Device for Measuring Reciprocal Time Intervals

Edward F. MacNichol and Jay A. H. Jacobs

Rev. Sci. Instrum. 26, 1176 (1955); http://dx.doi.org/10.1063/1.1715216 (5 pages) | Cited 13 times

Online Publication Date: 29 December 2004

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A device is described which converts a train of electrical impulses into a succession of hyperbolic wave forms of amplitude proportional to the interval between successive impulses. These wave forms when applied to an oscilloscope furnish a display capable of showing rapid changes in the frequency of an electrical signal. Unlike conventional counting‐rate meters response to sudden changes in frequency is immediate so that averaging over several cycles is not required. The instrument as constructed operates in the lower audio‐frequency range and is being used in the study of the electrical discharge of single fibers of the optic nerve.

Magnetic Suspension Balance

J. W. Beams, C. W. Hulburt, W. E. Lotz, and R. M. Montague

Rev. Sci. Instrum. 26, 1181 (1955); http://dx.doi.org/10.1063/1.1715217 (5 pages) | Cited 26 times

Online Publication Date: 29 December 2004

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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.

Large Scintillators as Threshold Detectors for High‐Energy Processes

J. J. Thresher, C. P. Van Zyl, R. G. P. Voss, and R. Wilson

Rev. Sci. Instrum. 26, 1186 (1955); http://dx.doi.org/10.1063/1.1715218 (6 pages) | Cited 6 times

Online Publication Date: 29 December 2004

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The design is described of several liquid organic scintillation counters which have been used to detect 100‐Mev neutrons and gamma rays with the exclusion of lower‐energy particles and quanta.
The neutron counter efficiency is a few percent and is nondirectional, properties not possessed by a more conventional counter telescope system. The gamma‐ray counter has an efficiency of about 50%, with a line width of about 10%.
Particular problems arise in the use of these counters; counting rate stability is difficult to achieve; the maximum counting rate is limited by the pileup of individual pulses due to their finite width. These problems are discussed in detail and some solutions mentioned.

Millimicrosecond Timing with Large Scintillation Detectors

J. W. Keuffel, W. H. Sandmann, and R. K. Stitt

Rev. Sci. Instrum. 26, 1191 (1955); http://dx.doi.org/10.1063/1.1715219 (5 pages) | Cited 2 times

Online Publication Date: 29 December 2004

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The timing precision attainable with large liquid scintillation detectors has been studied. Such detectors have slow rise‐times (∼10−8 sec) compared with those used in conventional nuclear physics timing experiments. The rise‐time is a result of photon time of flight and transit time in the larger, slower photomultipliers (such as the Dumont 6364) which must be used for good light collection. However, timing errors due to rise‐time may be largely overcome when dealing with large, statistically smooth pulses such as are encountered in cosmic‐ray experiments with unstable particles. A simple correction based on the pulse height is applied to each time measurement. Using this technique a timing error curve is obtained with a standard deviation of 1.6 mμsec for a large detector using a Dumont 6364.

Simple Humidity Lag Apparatus

Saburo Hasegawa, Samuel B. Garfinkel, and Arnold Wexler

Rev. Sci. Instrum. 26, 1196 (1955); http://dx.doi.org/10.1063/1.1715220 (2 pages)

Online Publication Date: 29 December 2004

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A simple apparatus for producing humidity step‐functions at room temperature, using saturated salt solutions to maintain constant relative humidities, is described. For an air flow of 200 lpm, the time required to change from one relative humidity to another is of the order of 30 to 50 milliseconds. This apparatus is particularly useful for establishing the lag characteristics of hygrometer elements.
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Measurement of the Screen Potential of Cathode‐Ray Tubes

E. E. Welch

Rev. Sci. Instrum. 26, 1201 (1955); http://dx.doi.org/10.1063/1.1715221 (1 page)

Online Publication Date: 29 December 2004

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