File:X rays and crystal structure (1915) (14778018695).jpg

Identifier: xrayscrystalstru00braguoft (find matches)
Title: X rays and crystal structure
Year: 1915 (1910s)
Authors: Bragg, William Henry, Sir, 1862-1942 Bragg, William Lawrence, Sir, 1890-1971
Subjects: Crystallography X-rays
Publisher: London : G. Bell
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: MSN

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wellto employ a thickness of 2 mm. over the whole ofthe box, and in addition a special shield of 5 mm.thickness on the side of the box next the apparatus.The bulb is mounted so that it can be adjusted to anexact position. The centre of the fine pencil of rayswhich emerges from a slit in the side of the boxshould pass exactly through the axis of the spectro-meter, and the source should be as nearly as possiblea line parallel to that axis. For this reason the bulbshould be so placed that the plane of the anticathodepasses very nearly through the slits; the pencil ofrays then leaves the anticathode at a grazing angle.A special form of bulb in which the anticathodeis perpendicular to the stream of cathode rays is THE X-RAY SPECTROMETER 23 especially convenient.* This arrangement greatlydiminishes the evil effect of any wandering of thecathode spot over the surface of the anticathode. The slit at A permits a fine pencil of rays to issuefrom the box. A second slit is often very useful ; in
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Fig. 4. the drawing it is shown at B, but on occasions it maybe placed as close to the crystal as possible. In thelatter case it is used to define the width of the X-ray * We owe the idea to Prof. R. W. Wood. 24 THE X-RAY SPECTROMETER pencil ; in any position it helps to cut off stray radia-tion. The crystal C is mounted on a revolvine tablecarrying- an arm, at the end of which is a vernierworking- in conjunction with a graduated circle. Theholder of the crystal is made to rock about a hori-zontal line, lying in the face of the crystal and passingthrough the centre of the spot where the rays strikeit. This permits adjustment in case the reflectingplanes of the crystal are found on trial to be out ofthe vertical. The crystal is mounted on a lump ofsoft wax, its position being generally determined bypressing the face to be used against a metal templatewhich is afterwards removed. The reflected pencil of X-rays passes into anionisation chamber mounted so as to be capable ofrevolving abou

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