Shield Electrode Research Articles

New Hot-Filament Ionization Gauge with Low Residual Current

The design and performance of a new type of hot-filament ionization gauge is described. The ions are extracted from the ionization region, focused through an aperture in a shield electrode, and then collected on a short, fine wire. The sensitivity factor of this gauge is about 13 Torr−1 for nitrogen. The ratio of the soft x-ray flux reaching the collector of the new gauge to that of a Bayard-Alpert gauge is calculated, and the x-ray limit of the new gauge estimated to be 3×10−13 Torr. Measurements at low pressures indicate that the x-ray limit cannot be greater than 7×10−13 Torr and may be considerably less. False pressure indications, caused by the electronic desorption of positive ions from chemisorbed gases on the grid (in particular, oxygen), are at least 500 times smaller in the new gauge than in the Bayard–Alpert gauge.

A simple method for making spherical tungsten cathodes of various sizes

Spheres of 0.006 to 0.8 mm diameter are melted at the top of tungsten wires by electron bombardment. A shield electrode at cathode potential decreases current losses and a ring electrode at anode potential the electrostatic forces.

Ionization Vacuum Gauge with Photocurrent Suppression

A new ionization vacuum gage with suppression of the photoelectric current from the ion collector was developed for the measurement of very low pressures. The gage, which is similar to a standard Bayard-Alpert gage, includes a suppressor ring and a shield electrode. The shield eiectrode shields the suppressor ring, ion drift region, and collector region and forms an electrostatic lens with the grid for accelerating and focusing the ions on the collector. The gage is linear over the range of pressures of 10⁻⁶ to 10/ sup -10/ Torr. (D.L.C.)

An Oil-immersed X-ray Outfit for 500,000 Volts and an Oil-immersed Multi-section X-ray Tube

IN recent years there has been an ever growing demand for higher voltage x-ray equipment in both the medical and the industrial fields. An x-ray tube that must operate continuously day after day at high voltage and current requires a degree of dependability and reliability that is more exacting than is needed in types of tubes designed primarily for experimental work. Such tubes must require only the minimum amount of technical service and of operating attention to be a useful tool in medical and industrial application. They should never be operated up to the very limit of their capacity; they should be capable of operation at full load within a few moments from the time the operator has applied the voltage. Their electrical characteristics must be stable and reproducible and they must be free from occasional puncture of the insulating envelope. Operating delays caused by the necessity of prolonged aging, by instability, or by the occasional puncture of the insulating envelope, will become increasingly serious. Field Current Problem.—The field current problem is perhaps the most important limiting factor that determines the maximum voltage and current at which the tube can be safely operated. These currents are produced by electrostatic forces which are powerful enough to pull electrons out of cold metal surfaces. Field currents may cause unstable operation in any x-ray tube and may destroy the vacuum as well. The dangers of producing field currents at higher voltages may be minimized by a suitable choice of metal, by its proper heat treatment before assembly and during exhaust, and by suitable electrode and tube design. The harmful effects of these currents may be minimized and the voltage range may be widened by increasing the strength of the dielectric wall of the insulating envelope. This may be done by thickening the glass or porcelain wall, immersion in oil, or the use of a double wall vacuum jacket. The harmful effects of field currents may also be decreased by suitable electrode dimensions, and by electrode shielding, which decreases the chance of these random currents striking the insulating envelope. Multi-section X-ray Tube Construction.—Several years ago Dr. Coolidge (1) began the development of the multi-section construction in order to control better the field current problem in high voltage tubes. By intermediate electrodes between the cathode and anode the potential gradient across the tube could be better distributed. The maximum voltage between any adjacent pair of electrodes could thus be kept safely below values at which field currents might occur. We have had two tubes of this type in active operation in busy hospitals for three years, and they have been completely free from the field current problem. Figure 1 illustrates the construction of this type of tube which was built for operation in air at 800,000 volts. It consists of four sections with 200,000 volts applied to each.

Influence of Splanchnic Nerves on Gastric Secretion

Very little is known about the influence of the sympathetic nervous system on the gastric glands (Volborth and Kudryavzeff1), and the data concerning the effect of epinephrine on the gastric secretion are rather confusing (Lim,2 Ivy and Mcllvain,3 Sirotinin,4 Hess and Hundlach5).Experiments were performed on dogs and cats anesthetized with a mixture of chloralose and urethane. The splanchnic nerves were isolated below the diaphragm and placed on shield electrodes. The vagi were either cut at the neck or tied around the oesophagus below the diaphragm. The pylorus was ligated and a fistula placed in the posterior wall of the stomach and brought out in the left flank through a stab wound.Rhythmic stimulation of the splanchnics was carried out in this fashion for periods of 8 to 10 hours. In most of the experiments a secretion of thick alkaline mucoid fluid began during the first hour of stimulation and continued at a steady rate thoughout the experiment. In dogs of average weight (8 to 10 kg.) the hourly amo...

Experiments dealing with the relation of the sinus node to the effects of stimulation of the vagus nerves

Experiments by a number of investigators on the sino-auricular node have warranted the conclusion that this structure is responsible for stimulus production and the maintenance of the rate of the heart. Flack thought that this node formed a station in the pathway, both of the vagus and of the accelerator nerves, and that through its agency they exercised their influence on the heart. He attempted to show that exclusion of the node from function consequently interrupted impulses passing over the nerves.It is the purpose of this paper to report that a large number of experiments have been performed on dogs to determine the relation of the vagus nerves to the sinus node. The experiments were performed under ether; a small opening in the chest was made by resecting one or two ribs, and both vagus nerves were dissected, cut and laid on shield electrodes. Records were taken electrocardiographically. The results of stimulation of both vagus nerves were first registered. Then the sinus node was carefully clamped ...