Volume 22, Issue 7, July 1951
Index of content:
A Comprehensive Counting System for Nuclear Physics Research Part I. Basic System and Synthesis of Simple Instruments22(1951); http://dx.doi.org/10.1063/1.1745971View Description Hide Description
A majority of nuclear measurements involve digital pulse counting so that the associated instruments have many common functions. Further investigation reveals that these counting systems fall into two broad classes: Those in which all pulses exceeding a certain threshold are summed, and a more complex analyzing procedure wherein pulses must be classified according to amplitude or temporal distribution.
In the former class are found the orthodox scalers, while the latter defines the pulse amplitude analyzers and other machines capable of yielding spectral distributions.
It is found that such instruments may be synthesized from a common group of sub units, and these are outlined and listed on a functional basis.
While the utility of the sub units is evidently determined by their versatility, they are in addition required to have high reliability in order that complex assemblies may give satisfactory service. Design for long life follows naturally from the latter consideration.
The next section of the paper shows the manner in which the simpler instruments can be synthesized according to the proposed scheme and outlines the more complex automatic counting and analyzing systems to follow in later parts of the paper. In particular the construction of a range of scalers is illustrated and their performance specifications and photographs are shown.
22(1951); http://dx.doi.org/10.1063/1.1745972View Description Hide Description
An annular Geiger‐Müller counter with six anodes has been built as a replacement for the usual six‐tube charged particle shielding ring in a cosmic‐ray anticoincidence bundle. Experiments show that the multiple‐anode counter has uniform pulse heights and starting voltages on all anodes, and a slightly higher shielding efficiency than the six‐tube ring.
22(1951); http://dx.doi.org/10.1063/1.1745973View Description Hide Description
The general linear voltage stabilizer is specified by four independent performance parameters which are necessary and sufficient to determine its performance and an equivalent circuit of four elements is derived to represent it. Corresponding parameters for a stabilizer associated with a load are evaluated in terms of parameters of the stabilizer itself and the load resistance by means of this equivalent circuit. In the case of a stabilizer associated with a load and power supply, corresponding over‐all parameters are defined, and the general solution of the problem of expressing the over‐all performance parameters in terms of parameters of the stabilizer itself and the load and supply resistances is obtained. Prior results are based on three explicit performance parameters, and the case of the general stabilizer is tractable only by the use of a supplementary procedure to include a fourth parameter. The present results yield an analytical criterion for the case where the three‐parameter analysis applies directly and permit direct evaluation of over‐all performance parameters in the general case without reference to the internal configuration of the stabilizer. Confirmatory experimental results are presented.
22(1951); http://dx.doi.org/10.1063/1.1745974View Description Hide Description
In order to measure the effects of gross changes in the design of the pole and yoke for a large synchrocyclotron cheaply and conveniently, a model half‐magnet having a two‐inch diameter pole was constructed. From data on the fields produced by poles of various lengths using a fixed amount of copper in the coil, the pole length for which the cost of power and magnet steel was a minimum could be determined. Measurements of the efficiencies of poles of various shapes indicated that it would be possible to design a shimmed pole to have an efficiency of 70 to 75 percent at a field of 20,000 gauss. Finally data on over‐all magnet efficiency as a function of the ratio of the cross‐sectional areas of the yoke and pole permitted calculation of the ratio for which the cost of steel, copper, and power would be a minimum.
22(1951); http://dx.doi.org/10.1063/1.1745975View Description Hide Description
22(1951); http://dx.doi.org/10.1063/1.1745976View Description Hide Description
A bar‐magnet velocity meter for vibratory and shock motions has been investigated both theoretically and experimentally. There has resulted a set of characteristics which constitute a marked improvement over the characteristics of previous velocity meters, in important respects. The instrument consists of a long bar magnet which moves relative to a long coil. It is shown that Alnico V combines all the best features required of the magnetmaterial, when compared experimentally with a magnet made of hardened tool steel and theoretically with other grades of Alnico, Cunife, and tungsten steel. Different methods are discussed for installing the velocity meter.
22(1951); http://dx.doi.org/10.1063/1.1745977View Description Hide Description
22(1951); http://dx.doi.org/10.1063/1.1745978View Description Hide Description
An electronic power source for use in selective electrolysis or as a low voltage regulated supply is described. Its output is dc continuously controllable from zero to five volts at two amperes. Among its features are ripple content of 0.1 percent, and an output resistance of 0.01 ohm. The input impedance of the regulator circuit itself is in the order of 10 megohms, permitting control from high resistance electrodes.
The instrument uses a variable‐amplitude two‐kilocycle carrier which is amplified by a power stage and fed to a dry‐disk rectifier. The output is then automatically controlled for equality to a self‐contained adjustable reference voltage. With modifications in the high level stages, the circuit is adaptable to a wide range of output capabilities.
22(1951); http://dx.doi.org/10.1063/1.1745979View Description Hide Description
A discussion is given of the design considerations, operational procedures, safety devices, and performance of a small homogeneous reactor using enriched uranium in a water solution and beryllium oxide and graphite for the neutron reflector. A high power and a low power phase of this reactor are described.
22(1951); http://dx.doi.org/10.1063/1.1745980View Description Hide Description
Methods are described in which microwave techniques are used to measure the electron density during the period following a discharge. By measuring the detuning of a resonant cavity containing electrons, it is possible to measure electron densities between 1010 and 106 electrons/cc in gases whose pressure may be varied over a wide range. Design criteria are given to permit proper operation of the method under the conditions encountered in a given experiment.
22(1951); http://dx.doi.org/10.1063/1.1745981View Description Hide Description
The addition of an auxiliary quartz crystal to the usual composite piezoelectric resonator provides a convenient strain gauge, which simplifies the measurement procedure and permits the evaluation of amplitude dependent decrements over a wide range of strain amplitudes. A unique feature of the new procedure is that virtually instantaneous values of the decrement are obtained, thus bringing transient internal friction phenomena under observation. Mechanical resonance frequencies may be precisely determined for high as well as low decrement specimens. The numerical evaluation of terms is carried out for a recommended driver‐gauge construction of 18.5° X‐cut quartz bars.
22(1951); http://dx.doi.org/10.1063/1.1745982View Description Hide Description
22(1951); http://dx.doi.org/10.1063/1.1745983View Description Hide Description
A circuit capable of measuringalternating current potentials up to 1000 microvolts with a precision of 0.01 microvolt has been devised and applied to the measurement of the galvanomagnetic coefficients of semiconductors and metals. The circuit consists essentially of a peaked amplifier applied to the out‐of‐balance signal between an alternating current potentiometer and the potential being measured. The galvanomagnetic coefficients are so related to the potentials that the entire measurement becomes independent of the current. As an example of the results obtainable, data are given to show the variations of the Hall and magneto‐resistivity coefficients during the high temperature graphitization of index rod. The precision of the final data is of the order of one‐quarter percent.
22(1951); http://dx.doi.org/10.1063/1.1745984View Description Hide Description
A large beta‐ray spectrometer based on the theory worked out by Siegbahn, Svartholm, and others has been constructed. The magnet design is unique in that the return path in iron for the gap flux is provided by a circumferential yoke rather than by an axial core. The mean radius of the electron orbits is r 0=30 cm and the maximum acceptable solid angle with present diaphragms is 0.8 percent of a sphere. Construction is discussed and data are presented to show the resolution to be approximately 0.4 percent under these conditions.
- LABORATORY AND SHOP NOTES