. The principles and practice of roentgenological technique . Fig. ids.—Broad focus, high vacuum tube. APPEARANCE OF ACTIVATED GAS TUBE 83 The electrostatic charging of the walls ofthe tube, especially about the cathode resultsin a retention of the gas content but by theheating of the tube this retained gas is re-leased. In a tube normally energized an equil-ibrium is thus maintained and the vacuum re-mains fairly constant. If the current passingthrough the tube—does not heat the tube, theelectrostatic charging will result in elevationof the vacuum. But if the tube is heavilv The best method o
. The principles and practice of roentgenological technique . Fig. ids.—Broad focus, high vacuum tube. APPEARANCE OF ACTIVATED GAS TUBE 83 The electrostatic charging of the walls ofthe tube, especially about the cathode resultsin a retention of the gas content but by theheating of the tube this retained gas is re-leased. In a tube normally energized an equil-ibrium is thus maintained and the vacuum re-mains fairly constant. If the current passingthrough the tube—does not heat the tube, theelectrostatic charging will result in elevationof the vacuum. But if the tube is heavilv The best method of studying the phenomenain an activated tube is to photograph it,by means of a pin hole camera by the lightfurnished by the energized tube itself. Sucha photograph discloses more than is apparentto the eye. There is a division of theglass bulb into two zones, one in front ofthe target, brightly illuminated, and onebehind, which is relatively dark, with theexception of a greater or lesser glow about. Fig. io6.—The tube is too low for the production of x-rays. The bluish glow of the ionized gas isshown behind the target. energized for too long a period, a markedlowering of the vacuum will take place. Re-versal of the polarity raises the vacuum. The discoloration of the active half of thetube takes place with normal usage and doesnot affect the x-ray output but the pulveri-zation of the target with metallic deposit onthe glass absorbs a certain quota of the , reversing the polarity, which causesmarked sputtering should be avoided. As the tube hardens, the color changes toa light gray green, the division zone becomesindistinct and the hemispheres lack contrast. the accessory anode. The cathode shows itsbrightly glowing concave surface. The stemand the glass extension in which it is set aredark. In medium and low vacuum tubes afan-shaped, illuminated area coming from thecathode is visible. The cathode stream can be recognizedby the eye only in very soft tubes, but is
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradiogr, bookyear1920
