. A text-book of radiology . ndexpensive X-ray outfit without a suitable X-ray tube, and,what is equally important, in the charge of a person whoreally understands its vagaries. While the induction coil is in very common use byradiographers, it is by no means an essential as we shallsee subsequently—what we do require is a source of highpotential electricity, but this can be obtained in several ways. 31 32 TEXT-BOOK OF RADIOLOGY. It is for these reasons that we take up the study of thefocus tube first, and it is proposed to deal with it as fullyas the limits of a work of this size will allow.
. A text-book of radiology . ndexpensive X-ray outfit without a suitable X-ray tube, and,what is equally important, in the charge of a person whoreally understands its vagaries. While the induction coil is in very common use byradiographers, it is by no means an essential as we shallsee subsequently—what we do require is a source of highpotential electricity, but this can be obtained in several ways. 31 32 TEXT-BOOK OF RADIOLOGY. It is for these reasons that we take up the study of thefocus tube first, and it is proposed to deal with it as fullyas the limits of a work of this size will allow. We have already seen that the design of the modernX-ray tube, however much it may have been modified indetail since, is really due to Prof. Herbert Jackson, ofKings College, London. The original tubes, one ofwhich is here illustrated, were about five inches in lengthbetween the external electrodes and the bulb about twoand a half to three inches in diameter. At one end isseen the concave cathode directed towards a platinum. ■ ■■■■■■., Fig. 11. Original Focus Tube. disc—the anode or anti-cathode, which is inclined at anangle of about 45°, and so mounted that it is slightlybeyond the focal point of the cathode. This mounting ofthe anode just beyond the focal point is not so difficult asit might at first appear. The cathode rays, while coming to a focus off the sur-face of a concave disc just as ordinary light would froma mirror of the same shape, do not behave in the sameway after the focal point is passed. Ordinary light rays begin to diverge immediately—thecathode rays, on the other hand, appear to travel for somedistance as a thin pencil of parallel rays, after which theydiverge at approximately the same angle as that at whichthe convergence took place. CONSTRUCTION OF X-RAY TUBES. 33 This at least is what appears to occur and can bewatched in a very low vacuum X-ray tube—so low thatpractically no X-rays can be detected outside it. Undersuch conditions t
Size: 2274px × 1099px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidtextbookofra, bookyear1915
