. Elementary and dental radiography / by Howard Riley Raper . steel.(See Fig. 368.) Tubes of this design are capable of transmitting muchmore current than the ordinary tube without danger of puncturing in thecathode region. Tubes with cathode collars, which the writer has seenin operation, show a light ring in the inactive hemisphere giving the tubesomewhat the appearance of a tube with inverse current passingthrough it. The finer—i. e., the smaller—the focal point, the place where thecathode stream strikes the target, the more likely burning of the target X-RAY TUBES AND THE X-RAYS 337 is to
. Elementary and dental radiography / by Howard Riley Raper . steel.(See Fig. 368.) Tubes of this design are capable of transmitting muchmore current than the ordinary tube without danger of puncturing in thecathode region. Tubes with cathode collars, which the writer has seenin operation, show a light ring in the inactive hemisphere giving the tubesomewhat the appearance of a tube with inverse current passingthrough it. The finer—i. e., the smaller—the focal point, the place where thecathode stream strikes the target, the more likely burning of the target X-RAY TUBES AND THE X-RAYS 337 is to occur. Thus a tube with a very fine focal spot should have not morethan about 20 to 40 milliamperes sent through it, while the same sort ofa tube with a medium or broad focal spot may transmit 80 to 200 mil-liamperes without injury to the target. Tungsten targets are capable of withstanding much more heat thanplatinum targets. Figure 369 shows a ring in front of the target. The functions ofthe ring are: (1) To sharpen the focal spot. (2) To overcome the.
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