. Archives of physical medicine and rehabilitation . former be applied directly to the uni-versal Coolidge tube without the neces-sity of a noisy synchronous motor? Asa matter of fact, this can be doneprovided the largel is kept cool practice, however, there is no ob-jection to using the tube with the tar-get extremely hot. Now, once tungs-t n reaches the temperature of 2000C. (3300 C. is melting point) itbegins to emit electrons. This meansthat, with the target above this tem-perature, an inverse stream of electronsis present if no rectifying device isused. Such an inverse current n
. Archives of physical medicine and rehabilitation . former be applied directly to the uni-versal Coolidge tube without the neces-sity of a noisy synchronous motor? Asa matter of fact, this can be doneprovided the largel is kept cool practice, however, there is no ob-jection to using the tube with the tar-get extremely hot. Now, once tungs-t n reaches the temperature of 2000C. (3300 C. is melting point) itbegins to emit electrons. This meansthat, with the target above this tem-perature, an inverse stream of electronsis present if no rectifying device isused. Such an inverse current notonly gives rise to x-rays from regionsin the neighborhood of the cathode(where the inverse electrons hit), butalso because of the extreme heat de-veloped at the spot where the electronshit, increases the danger of a tubepuncture. (The danger signal in thiscase is the appearance of green fluor-escence in the neighborhood of thecathode.) With a universal tube,therefore, a rectifying device is neces-sary ; with the radiator tube, however, 1 ■! ■. for reasonscase. Maximum Input 72. The importance of the questionof permissible input should be evidentfrom the last paragraph. As in thecase of gas tubes, so in the type weare now considering, every tube has permissible input. The sup-ply of too much energy (volts x mil-liamperes x time) may melt the target,vaporize the metal, blacken the tubeand so increase the danger of tubepuncture. Moreover, in the case ofa tube used for the long intervals nec-essary in therapy, the heat radiatedfrom the hot target jnay cause a risein temperature of the glass bulb suffi-cient to liberate gas and possibly tomelt the glass. Fortunately, unlike thepractice in the case of gas tubes, themaximum input for each type of Cool-idge tube is clearly stated. For ex-ample, in the case of the 7 universaltube used for radiographic purposes,when operated with a voltage equiva-lent to a gap of 6 between points,the milliamperage should not exceed80 ma.
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