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Dec 1962

Volume 33, Issue 12, pp. 1313-1478

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Proportional Counting Technique for Radiocarbon Measurements

Reidar Nydal

Rev. Sci. Instrum. 33, 1313 (1962); http://dx.doi.org/10.1063/1.1717767 (8 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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A proportional counting system for radiocarbon dating is described in this article. The CO2 counter has an effective volume of 1.2 liters and operates at a pressure of 2 atm. The total background is 1.10 counts∕min and the standard net count on recent carbon is 16.0 counts∕min. Maximum measureable age is 43 000 years. The end terminals of the counter have a few original details which serve to reduce inactive counter volume and the end effects. The ground capacity of the center wire has been reduced to a very small value (10 pF). Anticoincidence shielding is provided by a multiple‐anode proportional counter. It is filled with C3H8 to a pressure of 1.3 atm and can operate continuously for at least one year without refilling. The counter walls of the ring counter and the CO2 counter are connected together and supplied with the same high voltage. Shielding against γ rays is provided by a 22‐cm‐thick iron shield around the counting unit, and by a shell of 3.5‐cm old lead between the CO2 counter and the ring counter.

Controlled Flash Heating of Metal Filaments

R. A. Pasternak, Edward C. Fraser, Björn Bergsnov‐Hansen, and H. U. D. Wiesendanger

Rev. Sci. Instrum. 33, 1320 (1962); http://dx.doi.org/10.1063/1.1717768 (4 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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A simple inexpensive instrument for flash heating metal filaments has been designed which is being used in studying sorption phenomena at very low pressures and in measuring heat capacities and total emissivities of metals. The instrument permits selecting both absolute heating rates and their time dependence; in particular, filament temperatures increasing linearly with time can be obtained. Furthermore, the heating circuit allows the attainment of a preselected maximum filament temperature without appreciable over‐shooting. This paper describes the concept and design of the device; detailed experimental results are being reported elsewhere.

Field Emission Spectrometer

Allan M. Russell

Rev. Sci. Instrum. 33, 1324 (1962); http://dx.doi.org/10.1063/1.1717769 (4 pages) | Cited 4 times

Online Publication Date: 29 December 2004

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An apparatus is described which measures the energy distribution of electrons extracted from solids, particularly semiconductors, by high electric fields. The energy spectra of these electrons are directly related to the location of allowed electronic states at the surface of the solid. Investigation of a range of energies and direct output of the energy spectra are obtained through the use of modulation and phase sensitive detection. Details of the spectrometer are described including samples of the output spectra.

A 170‐Liter Heavy Liquid Bubble Chamber

A. G. Prodell and J. Steinberger

Rev. Sci. Instrum. 33, 1327 (1962); http://dx.doi.org/10.1063/1.1717770 (4 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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A 170‐liter Columbia‐Brookhaven heavy liquid bubble chamber has been operated at Brookhaven National Laboratory in a magnetic field of 15 kG. The bubble chamber was designed with a retro‐directive system of illumination which produces bright field optics. Details of the chamber, the magnet, and the optical system are given.

Technique for the Measurement of Short Carrier Lifetimes

S. C. Choo and E. L. Heasell

Rev. Sci. Instrum. 33, 1331 (1962); http://dx.doi.org/10.1063/1.1717771 (4 pages) | Cited 4 times

Online Publication Date: 29 December 2004

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The phase shift method for the measurement of semiconductor carrier lifetime has been extended by the use of a light beam modulated at frequencies up to 4 Mc with a Kerr cell, to provide direct measurement of lifetimes down to at least 10−8 sec. Some typical results for the temperature variation of lifetime in indium antimonide are presented.

High Geometry Gas Cell Proportional Counter

J. D. Ludwick

Rev. Sci. Instrum. 33, 1335 (1962); http://dx.doi.org/10.1063/1.1717772 (3 pages)

Online Publication Date: 29 December 2004

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A 4‐chamber proportional counter was built with very thin windows to detect weak beta radiation in an external gas cell. The instrumental design permits relatively high counting efficiencies and also incorporates an anticoincidence background reduction feature inherent in the detectors' position, with respect to spurious cosmic‐ray produced events. Gaseous materials containing the weak beta‐emitting radioisotopes Kr85, C14, and H3 have been detected using this instrument. Over‐all counting efficiencies for these isotopes were 55%, 26%, and 1%, respectively. The specific activity of the material is calculated from PVT data in the sample cell. After calibration, the counter is useful as a means of secondary standardization or where impure gas samples must be tolerated.

Plasma and Ion Beam Characteristics of the Dynamag Ion Source

Edwin M. Kellogg and Karl E. Eklund

Rev. Sci. Instrum. 33, 1338 (1962); http://dx.doi.org/10.1063/1.1717773 (2 pages) | Cited 5 times

Online Publication Date: 29 December 2004

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A description of an ion source of the duoplasmatron type is given. Experimental results related to the plasma density distribution in the region between the intermediate electrode and the anode are given and discussed. Ion beam behavior in the extractor region as a function of extraction potential and total current has been studied. Also, ion beam space‐charge neutralization by secondary electrons has been looked for, but not observed under present conditions.

Duoplasmatron as a Vacuum Ultraviolet Light Source

James A. R. Samson and Helmut Liebl

Rev. Sci. Instrum. 33, 1340 (1962); http://dx.doi.org/10.1063/1.1717774 (4 pages) | Cited 14 times

Online Publication Date: 29 December 2004

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The radiation emitted from a duoplasmatron ion source has been investigated between 500 and 2000 Å. When the ion source is operated with hydrogen, the familiar hydrogen continuum is produced down to 1650 Å, followed by the many‐lined spectrum down to 900 Å, including the atomic Lyman alpha and beta lines at 1215.7 and 1025.7 Å, respectively. With argon the source emits a line spectrum down to 550 Å originating from excited neutral, singly, and doubly ionized argon atoms.

New Ratio Ratemeter

Robert Hindel

Rev. Sci. Instrum. 33, 1343 (1962); http://dx.doi.org/10.1063/1.1717775 (7 pages) | Cited 3 times

Online Publication Date: 29 December 2004

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A new continuous ratio ratemeter is described which gives a linear indication of the single‐channel rate divided by the sum rate. The effective time constant of response is derived and the first four statistical moments are calculated for random channel inputs. The predicted performance is verified by the Monte Carlo method and through experimental results. It is furthermore shown that the conventional linear ratemeter is a special case of the more general ratio ratemeter.

Electrodeless Plasma Conductivity Probe Apparatus

Robert A. Olson and Edmund C. Lary

Rev. Sci. Instrum. 33, 1350 (1962); http://dx.doi.org/10.1063/1.1717776 (4 pages) | Cited 9 times

Online Publication Date: 29 December 2004

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A means for measuring the electrical conductivity of a fluid without the use of electrodes has been developed. A probe, consisting of a cylindrical single‐layer solenoid enclosed within an insulating tube, is used in conjunction with an rf oscillator‐detector to measure the ohmic dissipation of a small amount of rf power in the fluid. The probe samples the conductivity of the fluid in its immediate vicinity, and may therefore be used to resolve conductivity profiles in an operating MHD device, for example. Since the surface of the probe is an insulator, it is possible that the influence of Hall effects and electrostatic sheaths may be effectively eliminated under certain conditions. Electrolytic solutions have been used in calibration of the instrument. Instrumentation has been developed for the application of the measuring technique to plasmas. Probes have been operated successfully in the positive column of a hydrogen glow discharge and in a 4500°F rocket nozzle flow.

Probe for the Measurement of Albedo Electron Flux in a High‐Energy Ion Beam

R. A. Hubach

Rev. Sci. Instrum. 33, 1353 (1962); http://dx.doi.org/10.1063/1.1717777 (2 pages)

Online Publication Date: 29 December 2004

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A probe has been developed to measure the flux of electrons traveling in a direction opposite to that of the ions in a high‐energy ion beam. The probe is of the Langmuir type and will ideally obey the Mott‐Smith, Langmuir theory for positive probe potentials. With this probe the albedo electron flux has been measured in a beam of 1‐ to 2‐kV cesium ions.

Vacuum Evaporation Source with Double‐Wall Cylindrical Graphite Heater and Nozzle Outlet

Ferdinand J. Hemmer and James R. Piedmont

Rev. Sci. Instrum. 33, 1355 (1962); http://dx.doi.org/10.1063/1.1717778 (3 pages)

Online Publication Date: 29 December 2004

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A resistance heated source is described which is capable of evaporating refractory materials in vacuo. Film thickness uniformity and deposition efficiency are improved through the use of a converging‐diverging nozzle at the crucible outlet. The source also features a double‐wall cylindrical graphite heater configuration which facilitates the reduction of heat losses and copper to graphite electrical connectors capable of operating over a large temperature range.

Constant Acceleration Transducer Employing Negative Feedback for Use in ``Mössbauer Experiments''

David Rubin

Rev. Sci. Instrum. 33, 1358 (1962); http://dx.doi.org/10.1063/1.1717779 (3 pages) | Cited 5 times

Online Publication Date: 29 December 2004

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A triangular voltage is integrated and the output current fed to a vibrator so as to produce linearly changing velocities. The output voltage of a velocity pickup coil is then compared to the triangular input voltage in a negative feedback arrangement which further linearizes the velocity.

Dynamic Magnetic Measurements by Use of Damped Oscillatory Fields

Tait Elder and William Barte

Rev. Sci. Instrum. 33, 1360 (1962); http://dx.doi.org/10.1063/1.1717780 (7 pages) | Cited 2 times

Online Publication Date: 29 December 2004

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Full magnetic hysteresis loops, obtained by underdamped discharge of a capacitor through a solenoid, were used to study loop distortion produced by eddy currents, protracted or delayed flux changes, and instrumental errors. Pulsed field loops obtained for γFe2O3 powder with 14 000‐Oe maximum field closely overlapped loops obtained statically with one‐tenth this field amplitude. In contrast, an apparent coercive force of 110 Oe was obtained with the pulsed field method for a sample of 0.158‐cm‐diam iron wire having a static coercive force of 3.6 Oe. Almost two‐thirds of the observed coercive force was attributable to eddy currents. Instrumental errors were less than 10 Oe and the residual coercive force was identified with the protracted flux change which has sometimes been attributed to magnetic viscosity in iron. Instrumental difficulties involved delay, distortion, or imperfect integration of high frequency components in detector coil signals, cumulative integration errors associated with low frequency components from nearly saturated specimens, and pickup. The detection system described is also suitable for quasistatic (slowly traced hysteresis loop) measurements.

Low Temperature Double Path Absorption Cell

F. J. Smith, J. K. Smith, and S. P. McGlynn

Rev. Sci. Instrum. 33, 1367 (1962); http://dx.doi.org/10.1063/1.1717781 (5 pages) | Cited 12 times

Online Publication Date: 29 December 2004

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A low temperature double beam absorption cell designed specifically for the Beckman DK, DK‐1, and DK‐2 is described. It may be used down to at least −196°C in quantitative measurements of visible and ultraviolet absorption spectra of liquid or rigid glass solutions. A detailed listing of low temperature glasses and low temperature solvents which might be used in conjunction with the cell is given. In addition, some possible cooling systems are included.

Theoretical Study of Slit Scattering

Edward J. Burge and David A. Smith

Rev. Sci. Instrum. 33, 1371 (1962); http://dx.doi.org/10.1063/1.1717782 (7 pages) | Cited 10 times

Online Publication Date: 29 December 2004

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An expression is derived for the flux of multiply scattered charged particles emerging from a square‐edge collimating slit for a parallel beam at normal incidence. Full allowance is made for the continuous energy loss in the slit material, and the results are compared with those from Courant's theory. The effective increase in aperture is calculated for 50‐MeV protons on elements throughout the periodic table and the optimum materials for collimators are discussed. A computation of the origin on the collimator face of the slitscattered flux from 50‐MeV protons on copper shows that over 90% originate in the first 0.025 cm from the edge, when all energies are detected, and in less than 0.01 cm for energies above 37.5 MeV. The energy distribution is calculated as a function of the angular range accepted. The projected angle distribution, integrated over all energies, is found to have a maximum at about 1.5° for carbon, 4° for copper, and 7° for lead, with 50‐MeV incident protons. The higher energy slit‐scattered protons are shown to peak at smaller angles. Approximations in the theory are discussed and the results compared with those from Monte Carlo calculations by Becker and from the work of Överås.

Floating Zone Growth of Single Crystal Alkali Halides

Roger W. Warren

Rev. Sci. Instrum. 33, 1378 (1962); http://dx.doi.org/10.1063/1.1717783 (9 pages) | Cited 7 times

Online Publication Date: 29 December 2004

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A general discussion is given of the main factors affecting the successful attainment by induction melting of stable floating zones in a wide variety of materials. The emphasis is on poor conductors, for which the problems involved can usually be solved. Details of the apparatus and procedures used in the floating zone growth of NaCl, KCl, KBr, KI, and LiF single crystals are given, as well as specifications of the quality of such crystals as determined by various tests.

Circuit for the Rapid Determination of Langmuir Probe Data

F. W. Crawford and R. S. Harp

Rev. Sci. Instrum. 33, 1387 (1962); http://dx.doi.org/10.1063/1.1717784 (5 pages) | Cited 6 times

Online Publication Date: 29 December 2004

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The frequent use of Langmuir probes in the determination of electron temperatures and number densities in plasmas makes it desirable to have rapid methods of data reduction. This paper describes a simple and accurate instrument for carrying this out without the necessity of using logarithmic amplifiers or oscilloscope displays. Apart from its advantages in ease of construction, its calibration is particularly simple and drift‐free. In operation, the device samples the probe characteristic at two values of current, and yields a numerical value for the electron temperature on a meter. Linearity of the characteristic is examined by varying the sampling currents. Provisions are made for ion current to be compensated and measured, and for the electron saturation current to be estimated.

Tunnel Diode Decade Counter

B. Rabinovici

Rev. Sci. Instrum. 33, 1391 (1962); http://dx.doi.org/10.1063/1.1717785 (2 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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A decimal coded binary counter is described which employs four tunnel diodes to achieve ten stable states and a transistor circuit for reset amplification and readout of the carry. The tunnel diodes must satisfy certain relationships between their peak and valley currents and final voltages. The principle of operation is discussed and the circuit of the decade counter described. The paper presents the required conditions for the diode parameters and gives experimental results obtained on a laboratory model.

X‐Band Resonant Cavity for Optical Studies at Liquid Helium Temperatures

K. E. Rieckhoff and R. Weissbach

Rev. Sci. Instrum. 33, 1393 (1962); http://dx.doi.org/10.1063/1.1717786 (4 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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A detailed description of a cylindrical reflection cavity operating in the TE112 mode in the X band is given. The special features of the cavity design are provision for the passage of a beam of light through the region of maximum magnetic field in any direction perpendicular to the axis of the cavity, and an integral crystal mounting arrangement that allows optical alignment of the crystal around two perpendicular axes while the cavity is immersed in a liquid helium bath under reduced pressure.

Self‐Sampling System for Measurement of Picosecond Pulse Characteristics

Dimitrios C. Agouridis

Rev. Sci. Instrum. 33, 1396 (1962); http://dx.doi.org/10.1063/1.1717787 (3 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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The self‐sampling system utilizes the sampling of a pulse by itself for measurements of the pulse characteristics. The system can be used to measure characteristics of pulses rising in substantially less than one nanosecond. The pulse being measured is initially split into two pulses by a power divider. Then the two pulses so formed are delayed unequally as they propagate in separate transmission lines. Finally the pulses are brought together in the coincidence circuit which consists of a power divider and a wide‐band crystal detector. The operation of the system is based on the square law characteristics of the crystal detector. From the variation of the output of the coincidence circuit with variation in the delay difference, information can be obtained about the pulse amplitude, the pulse width, and the sum of the pulse rise and fall times. This system has been used to measure the characteristics of subnanosecond rise and fall time pulses generated by a mercury switch pulse generator.

Calculation of the Optimum Dimensions of Collimators for Neutron Diffraction

Ian R. Jones

Rev. Sci. Instrum. 33, 1399 (1962); http://dx.doi.org/10.1063/1.1717788 (3 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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If the horizontal angular divergence and total width of the aperture are preset, the neutron intensity transmitted by a primary Soller collimator will vary with the number of channels. For a given set of collimator system dimensions there is an optimum number of collimating channels, and a corresponding maximum in the transmitted intensity. For a broad range of system dimensions, it is possible to calculate both of these quantities explicitly. This provides a simple and rapid means of comparing alternatives in collimator design and location, for both optimal and nonoptimal configurations.

Display of Rotational Switching Characteristics of Magnetic Thin Films

J. P. Smith

Rev. Sci. Instrum. 33, 1401 (1962); http://dx.doi.org/10.1063/1.1717789 (5 pages) | Cited 4 times

Online Publication Date: 29 December 2004

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The apparatus and techniques for displaying both rotational critical curves and rotational hysteresis curves are described. The use of large values of 20‐kc control fields and linear circuitry enables the oscilloscope display of these curves to be directly related to the rotation of thin‐film magnetization. The degree of deviation of switching properties of actual magnetic films from those of the theoretical model can conveniently be determined from the oscilloscope display.

Negative Feedback Electrometer Circuit

Robert A. Spangler

Rev. Sci. Instrum. 33, 1406 (1962); http://dx.doi.org/10.1063/1.1717790 (4 pages) | Cited 6 times

Online Publication Date: 29 December 2004

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An electrometer circuit, utilizing a commercially available differential operational amplifier, is described and its basis of operation briefly analyzed. By virtue of the negative feedback configuration employed, interelectrode potential relationships in the electrometer tube are maintained virtually constant, thus providing highly stable performance, linear gain characteristics, and a high effective input impedance. Provision for compensation of nonideal amplifier characteristics and input capacitance neutralization is included.

A 4π Positron Scintillation Spectrometer

J. I. Rhode and O. E. Johnson

Rev. Sci. Instrum. 33, 1410 (1962); http://dx.doi.org/10.1063/1.1717791 (12 pages) | Cited 1 time

Online Publication Date: 29 December 2004

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A 4π scintillation‐spectrometer system applicable to the measurement of positron spectra is described. It is comprised of a 4π beta‐ray detector (two plastic scintillators), three gamma‐ray detectors (NaI crystals), and associated pulse‐height analysis and coincidence circuitry. Source techniques, calibration procedures, and various pertinent experimental considerations essential to its operation are presented. An evaluation of the system is made on the basis of its performance in the measurement of both positron spectra (Zn65 and Na22) and negatron spectra (Pm147 and W185). The implications of the experimental results obtained from beta spectra concerning a possible nonlinearity at low energies (<50 keV) in the scintillation response of the plastic phosphor to electrons are discussed.
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