File:Radiography, x-ray therapeutics and radium therapy (1915) (14570864179).jpg

Identifier: radiographyxrayt00knoxuoft (find matches)
Title: Radiography, x-ray therapeutics and radium therapy
Year: 1915 (1910s)
Authors: Knox, Robert, 1868-1928
Subjects: Radiography Radiotherapy X-rays
Publisher: London : A. & C. Black
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: MSN

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is open to question. When it is necessary to check thereverse current which is found when very heavy discharges pass througha tube a number of these valve tubes may be placed in the circuit. Regrulation of the Valve Tubes.—The regulation of valve tubes iseffected in a similar way to that of X-ray tubes, according to the type of regu-lator in use. In the case of the mica or carbon patterns, the lead which isnormally attached to the plate (anode), should be attached to the ring of theregulator, and current passed until the blue appearance has been restored tothe valve tube. The lead must then be reconnected to the anode terminal. 52 EADIOGRAPHY Valve tubes should never be worked hard. An intermediate vacuum,giving a Geissler discharge in the body of the tube, with a slight apple-greentint round the spiral base, wall be found best. Do not forget also, that a■ hard valve tube may be emitting an appreciable quantity of Rontgenrays, with a consequent need of protection for the operator.
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Fig. 48.—Gundelach valve tube. (Siemens.) Bauer Air-valve.—The latest improvement in the valve tube is the intro-duction of a Bauer air-valve for the regulation of the vacuum. This isvery useful and easily handled by the use of a small hand-pump, a longrubber tube allowing of regulation from a distance. When intensive currents are used it may be necessary to put a valvetube on each pole or even to have 6 or 8 valve tubes in series. By usingvalve tubes the amount of inverse current can be practically abohshed whenmedium currents are employed, but when very heavy currents are used it isnot possible, or hardly ever possible, to abohsh it. There are several other varieties of valve tube of more recent construc-tion. The various types described are useful on installations of mediumpower, but if they are used on the more powerful installations of recent date,they soon begin to vary in hardness, and add considerably to the difficultiesof the radiographer. This is particularly noticeable

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