Cathode Diameter Research Articles

Recent Developments in Multiplier Phototubes

A number of developments on multiplier phototubes have taken place in these laboratories since the last scintillation counter symposium. The most important of these developments are discussed and detailed operating data on various tubes are presented. One development of interest has been the large area multiplier phototubes. These tubes have been constructed with usable cathode diameters of ll inches, 142 inches, and 20 inches. On the other extreme, ten stage multiplier phototubes with an over-all outside diameter of 3/4 inches have been developed and the characteristics of these tubes will be presented. A program of ruggedization of multiplier phototubes has been carried out on all standard tubes and the results of this program have led to tubes with better mechanical stability in the field. Work is also described on cathode surfaces, on secondary emission surfaces, and on improvements of the dark current characteristics of multiplier phototubes.

Characteristics of the High Current Tungsten Arc in Argon, Helium, and Their Mixtures

An experimental study was made of the properties of the high current dc electric arc in argon, helium, and their mixtures at atmospheric pressure. Tungsten-rod electrodes were used over a current range from 10 to 100 amperes. Measurements of the voltage-current and the voltage-electrode separation characteristics were made along with the plasma voltage gradients in both the pure gases and in the mixtures. It was found that this type of arc was very stable when the system was free from oxide impurities and that the cathodic processes played a major role in the arc mechanism. The results obtained suggest that the value of the anode voltage drop for the inert gas arc over the current range studied is negligibly small. At the higher currents or with smaller diameter cathodes, tungsten was able to evaporate from the cathode in sufficient quantities to influence the character of the discharge. It was observed that the properties of the arc in mixtures of gases were in between the properties observed in the pure gases. The lower ionization potential gas, argon, had more effect on the properties of the arc in mixtures than did helium. As long as there was at least 15 percent argon present in the mixture, the arc properties and appearance were more like those observed in argon than in helium.

Note on Space-Charge Considerations in Test-Diode Design

A computation has been made of the conditions for choice of anode and cathode diameters in test diodes that will give the minimum variation in the slope of the space-charge line with small variations in tube geometry.

Determination of Radioactive Content of Rocks by Means of Geiger-Müller Counters

During a survey of the Velence Mountains in Hungary the authors developed a direct approximating method for use in determining the radioactive content of rocks by means of a Geiger-Mueller counter. The calibration method used is outlined and the calibration obtained can be expressed by the following approximate numerical formula: c = 2.4 . 10/sup -5/ J/LD, where c is the concentration in g-Th-equivalents/g of rock; J, the counting rate (in min); L the length; and D the diameter (in cm) of the brass cathode of the counter tube. Similarly the concentration in g-U-equivalents/g of rock can be expressed by the approximate numerical formula: c = 1.4 . 10/sup -5/ J/LD. The use of the following roughly approximating simple rule may be suggested for uranium explorers when extended territories must be surveyed within a short time: if a G-M counter of any commercial dimensions, shielded by 2 mm of lead, is placed against the rock wall and the observed counting rate (minus cosmic radiation) is x times the rate of cosmic radiation for the same counter, then the average U concentration in the rock is x times 25 g U/metric ton (1,000 kg) of rock.

A Study of Small Ether-Argon Geiger-Müller Counters

A variety of ether-argon mixtures were tried in counters with cathodes ranging in diameter from 0.268″ to 0.038″ and with wires ranging in diameter from 2.3 mils to 0.5 mil. The results suggest an optimum relationship between cathode diameter, wire size, and mixture. Good characteristics were obtained with cathodes as small as 0.067″ in diameter. Small probing counters designed on the basis of this relationship are described.

LVIII.Some experiments on the auto-electronic discharge

Summary A clean tungsten cathode of small diameter was produced by burning out a tungsten filament. The auto-electronic currents from this cathode in a high vacuum were reproducible. The currents were decreased by hydrogen and still more by air ; they were increased by coating the cathode with barium. It is concluded that auto-electronic currents are not due to gas, but that they depend on the nature on the cathode in somewhat the same way as the thermionic emission.