![]() The primary ways that X-ray tubes differ involve the construction of the target and the design of the regulator. Adding one or two special appendages to the tube (regulators or regenerative devices) helped control the gas pressure inside the tube. Making the target more massive was the primary method used to prevent it from overheating. Perhaps the most important were an overheating of the target when the tube was under heavy use, short and long-term variability in the gas pressure, reversals in the direction of the current through the tube (inverse discharges), and electrical discharges that might puncture the glass wall of the tube. Several problems had to be overcome when designing the tubes. For therapy, less penetrating X-rays were desired. For diagnostic imaging, more penetrating X-rays were preferred. The higher the applied voltage, the higher the energy of the X-rays, and the more penetrating they became. The greater the current (on the order of a milliamp) supplied by the operator to the tube, the greater the intensity of the emitted X-rays. When the electrons struck the target, X-rays were emitted. If the tube had no anticathode, the anode almost always served as the target. If the tube had an anticathode, it was the target. When a sufficient electric potential (high voltage) is applied across the tube's electrodes, a stream of electrons (aka cathode rays) travels through the gas from the cathode to the target. Tubes with both an anode and anticathode were often referred to as bi-anode tubes. It was not unusual for X-ray tubes to have three electrodes: a negatively charged cathode, a positively charged anode, and what was known as an "anticathode." The latter (aka auxiliary anode) was usually given a positive charge, but it sometimes had no electrical charge at all. The configuration of these tubes varied, but there were always at least two electrodes (an anode and a cathode) that might, or might not, be located at opposite ends of tube. Tubes designed for X-ray work usually contained air, although some (e.g., Snook tube) employed helium or hydrogen. Depending on the type of tube, the residual gas might or might not be air. What these different tubes had in common was the fact that they were made of glass and were partially evacuated. But at the time they were being manufactured, they were simply known as X-ray tubes. Today, gas discharge X-ray tubes are commonly referred to as “cold cathode” tubes in order to distinguish them from “hot cathode” Coolidge X-ray tubes that employ a heated filament. ![]() ![]() After the discovery, new types were developed that were specially designed to produce X-rays. The figure below from the 1914 catalog of the Otto Pressler company is so similar to the example in the collection that it is hard not to conclude that our tube was manufactured by Pressler.Prior to Roentgen’s discovery of X-rays in 1895, many different types of gas discharge tubes were already in use (e.g., Geissler, Crookes, Hittorf, Lenard tubes). 142 2014).Įach paddle in our tube has fluorescent strips that glow when struck by electrons-cool. Humphrey’s “A Century-Old Question: Does a Crookes Paddle Wheel Cathode Ray Tube Demonstrate that Electrons Carry Momentum?” (The Physics Teacher Vol. For more information about this topic, please check out T.E. Thompson, the turning of the wheel was due to the radiometric effect, i.e., the heating of the gas molecules adjacent to the area of the paddles being struck by the cathode rays. As explained by the “discoverer” of the electron, J.J. While the tube’s cathode rays (electrons) do possess momentum, the latter is not sufficient to turn the paddles. This movement was originally believed to demonstrate that the cathode rays possessed momentum that they transferred to the paddles. When high voltage is applied across the tube, the paddle wheel travels along the glass "railway track" from the cathode towards the anode. This type of gas discharge tube (aka paddle wheel tube) was invented in the 1880s by William Crookes as part of his investigations into the nature of cathode rays (electrons). ![]()
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