Index of content:
Volume 30, Issue 4, April 1959
30(1959); http://dx.doi.org/10.1063/1.1716522View Description Hide Description
The first U. S. satellite, 1958 Alpha (Explorer I) carried instrumentation to measure cosmic‐ray intensity, micrometeorite impacts, and temperatures within the satellite. The instrumentation was designed with emphasis on conservation of electrical power, on stable and reliable operation, on operation over a wide range of temperatures, and on compactness and mechanical ruggedness.
The cosmic‐ray instrumentation in 1958 Alpha operated according to expectations, providing several hundred recordings of data received during transits over ground stations. These data led to the discovery of a belt of high‐intensity radiation around the earth.
30(1959); http://dx.doi.org/10.1063/1.1716523View Description Hide Description
A large volume expansion chamber (25‐cm diameter, 25 cm deep) was constructed to investigate prebreakdown ionization processes in gaseous discharge. A homogeneous field electrode system was mounted within the chamber and provision was made for irradiation of the cathode. The chamber could be operated automatically at pressures from 40 to 68 cm Hg with a recycling time of about 5 min. Associated circuits for the production of millimicrosecond pulses up to 70 kvp are described. Some preliminary photographs of point‐plane breakdown and of electron avalanches in a homogeneous field electrode system are shown.
30(1959); http://dx.doi.org/10.1063/1.1716524View Description Hide Description
A field‐plotting and ray‐tracing technique based on electron‐optical methods is developed for first‐order ion optics of slit lenses and is applied to a Nier‐type thick lens. A resistance paper analog gives the distribution of electrostatic potential. Maxwellian velocities of ions emitted from the filament and lens thickness affect ion trajectories, which are calculated to a few percent accuracy by a simple approximation technique. Paraxial ray paths are shown and the ion‐focusing action of the single filament is described. Optimum detectability, 100 counts of the smallest isotope, is 5×10−15 g for uranium and 2×10−15 g for plutonium. Ionization at moderate temperatures improves transmission and avoids background impurities which appear at temperatures above 2000°C. Independent electrostatic focusing in the z direction improves transmission through the analyzer.
30(1959); http://dx.doi.org/10.1063/1.1716525View Description Hide Description
A random number generator which uses two 2000‐Mc subharmonic oscillators is described. This generator can produce random binary digits at a maximum rate of approximately 3×107 digits per second. Statistical tests performed on over a quarter‐million digits produced by this generator indicate that they were at least as random as digits produced by other slower contemporary means.
30(1959); http://dx.doi.org/10.1063/1.1716526View Description Hide Description
A method has been devised for introducing reference marks in stacks of nuclear emulsion pellicles by the use of single‐strand threads. The reference marks are then used for accurate lining‐up of the stack after development. Details of the thread insertion and lining‐up processes are described.
30(1959); http://dx.doi.org/10.1063/1.1716527View Description Hide Description
A method is presented for the determination of the coefficient of thermal expansion of solids, particularly in the low‐temperature region. The method is based on the measurement of the resonant frequency of one or more modes of a microwave cavity made of the material for which the coefficient of expansion is required. A change in length of 5 parts in 106 can be detected. This accuracy is primarily determined by the Q of the resonant cavity. Measurements of the thermal expansion of copper and bariumtitanate are presented over the temperature range of −200 to +100°C and the former is compared with observations made by other techniques.
30(1959); http://dx.doi.org/10.1063/1.1716529View Description Hide Description
A recording pyrometer which measures the brightnesstemperature at 0.65 μ of a small incandescent sample in the range 1300°C to above 3000°C with a time constant of a few milliseconds is described. The instrument, designed to be used in studies of materials exposed to the plasma jet of a high‐intensity electric arc, is reliable to within ±20°C, and is suitable for measuring transient high‐temperature fluctuations or for applications where use of a standard optical pyrometer might be hazardous to personnel.
30(1959); http://dx.doi.org/10.1063/1.1716590View Description Hide Description
A general expression for the solid angle subtended by a circular disk is derived in terms of complete elliptic integrals of the first and third kind. The elliptic integral of the third kind is reduced in terms of Heuman's lambda function, which has been tabulated. By transformation of the double integral Ω = ∫ ∫ sinθdθdβ into a single line integral, the solid angle can be conveniently determined. Since the solution involves only tabulated functions, it is well suited for desk calculation.
30(1959); http://dx.doi.org/10.1063/1.1716591View Description Hide Description
A vacuum‐type gas‐flow calibrator was designed and constructed for making accurate calibrations of flowmeters needed for the investigation of high‐pressure flames. This calibrator operates by automatically measuring the time required to pressurize a known volume from a near vacuum to 1 atmosphere pressure. The gas volume flow rate is obtained by dividing the calibration volume by the pressurization time and applying corrections from PVT data. This apparatus has been successfully used to calibrate flowmeters for use with hydrogen, oxygen, nitrogen, air, methane, nitric oxide, carbon monoxide, and various homogeneous nonexplosive gas mixtures.
30(1959); http://dx.doi.org/10.1063/1.1716592View Description Hide Description
An ion source has been developed, using strong‐focus principles, with a view toward obtaining high transmission through sector‐shaped magnetic fields. The lens described, starting with an ion beam 0.375 in. square, produces a line focus 0.60 in. long and 0.025 in. wide, with a half‐angle of divergence beyond the crossover of 0.034 rad.
30(1959); http://dx.doi.org/10.1063/1.1716593View Description Hide Description
This note describes an ac bridge for measuring the series components of high‐impedance metal‐liquid interfaces. The real and imaginary components of the impedance may vary over a wide range. All frequency‐independent residual error‐introducing elements in the measuring circuit may be balanced out through a single square‐wave initial balance step. This allows accurate, direct‐reading measurement of the unknown. The bridge design is based upon superposition of frequency‐independent bridge circuits.
30(1959); http://dx.doi.org/10.1063/1.1716594View Description Hide Description
Formulas are derived for the longitudinal and lateral momentum kicks to which a particle is subjected upon crossing an accelerating gap. The angle ε between the particle's trajectory and the axis of the accelerator tube is assumed to be small, and terms of order higher than the first in ε are neglected in the formulas.
30(1959); http://dx.doi.org/10.1063/1.1716595View Description Hide Description
A comparison has been made between natural muscovite mica and synthetic fluor‐phlogopite mica with regard to their usefulness as neutronmonochromators. It has been found that a synthetic mica monochromator reflects a neutron beam which is from 2 to 6 times more intense than that from a natural mica monochromator, while requiring no appreciable sacrifice in resolution. The interplanar spacing of the synthetic material was found to be 9.963 A, which is slightly larger than that of the natural mineral.
30(1959); http://dx.doi.org/10.1063/1.1716596View Description Hide Description
An improved rf unit for a nuclear magnetic resonancespectrometer is described. It uses a crystal oscillator for frequency stability and positive feedback from a cathode follower to increase the effective Q of the sample rf coil. This unit provides an rf level range of 20 μv to 60 mv with little limitation on extending the range. This allows saturation studies. The circuit is well suited to direct relaxation timemeasurements.
30(1959); http://dx.doi.org/10.1063/1.1716597View Description Hide Description
Description of an electric system which randomly closes one of two alternate circuits. The system is based upon the coincidence of two timing events of different origin. The sign of the coincidence signal varies at random and causes one of two thyratrons to fire. A statistical analysis shows that for 339 succeeding operations of the instrument the maximum deviation from complete randomness and independence of succeeding events is about 2%, the average deviation about 1%.
30(1959); http://dx.doi.org/10.1063/1.1716598View Description Hide Description
The integrator consists of a circuit which operates relays to turn off data‐storage devices, timers, etc., when the charge conducted by an ion beam reaches a specified quantity. A vibrating‐reed electrometer (without feedback) senses when the potential drop across a capacitor into which the beam current flows becomes equal to the potential of several standard cells in series. Errors in sensing the potential are less than 0.001%, and the over‐all time delay of the relay operation is about 15 msec. The major sources of error are associated with soakage and changes in capacitance with temperature, less than 0.05% and about −0.01% per °C, respectively. It should be feasible to attain a considerable reduction in all the errors of integration caused by these known sources of error.
30(1959); http://dx.doi.org/10.1063/1.1716599View Description Hide Description
With liquid hydrogen as the track sensitive medium, electron tracks were observed from 26.1 to 28.9°K. Using liquid deuterium, the range was 30.5 to 32.6°K. The upper limits in both cases were imposed by the apparatus. Data on expansion pressures, sensitive times, and refrigerant consumption are presented.
30(1959); http://dx.doi.org/10.1063/1.1716600View Description Hide Description
A pulse‐height discriminator has been developed which is capable of operating at repetition rates up to 10 Mc. It accepts positive input pulses with a threshold adjustable from 1 to 11 v. The output signal is of constant shape and amplitude. The circuit is described and test results are given.
30(1959); http://dx.doi.org/10.1063/1.1716601View Description Hide Description
This paper describes a 22‐Mev electron linear accelerator of the traveling‐wave type with several unique features. The features include the combination of an rf driven prebuncher cavity and a buncher of a new type in the first section of accelerator guide in order to obtain high‐peak currents and minimum beam energy spread. A separately pulsed gun grid provides fast beam pulse rise time for use in neutron research. The accelerator and major electronics are housed in a single rf shielded rigid cabinet, which facilitates portability for field operations. The beam energy is continuously variable from 2 to 27 Mev; peak current for a one‐μsec pulse is 380 ma; pulse rate is variable from 1 to 200 pulses per second; pulse length is variable from 0.2 to 2.4 μsec; and pulse rise time is adjustable from 0.2 to 0.4 μsec.