General Electric CA-2 X-ray Diffraction Tube (ca. 1930s) |
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| This is a General Electric Model CA-2 tube designed for x-ray diffraction analysis. I don't know what the "CA" stands for (crystalline analysis ?), but the "2" indicates that this a fine to medium focus tube. It would typically be operated at a potential of 30 kVp with a 20 mA current. The maximum rating for continuous operation was 42 kVp with a 25 mA current. |
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As seen above, the molybdenum target (mounted in the copper anode towards the left side of the photo) is positioned at right angles to the electron beam. In tubes designed for medical applications, the target is usually sloped so that the x-rays leave one side of the tube in a conical beam. In contrast, this design results in a uniform emission of x-rays in all directions in the flat plane of the target. That is why the cathode filament is a flat spiral similar to that in "Universal" tubes rather than the more common "Benson" style coil. The brownish ring formed in the glass envelope indicates the path by which the x-rays exit the tube. For x-ray diffraction analysis, the x-ray beam needs to be nearly monoenergetic. This is accomplished by using the target's characteristic x-rays and filtering out the bremsstrahlung. The cathode (not visible) is a spiral coil similar to that used in the early "Universal" x-ray tubes. It is located in the hemispherical focusing cup just to the right of the target. The two projecting connections seen on the left end of the tube in the top photograph would be connected to the cooling water supply. With water cooled tubes like this, it was common to operate the anode In the bottom photo, notice that the glass stem holding the wire leads for the cathode is made of yellow uranium glass. Size: approximately 19" long, 2.5" diameter (max) References: General Electric X-ray Corporation. Coolidge X-ray Tubes - Kenotrons. Bulletin No. 293. 1934. Kindly donated by Margie Wheaton in memory of her father Dr. Julius E. Marfy |
