File:X rays and crystal structure (1915) (14777669692).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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had therefore itself adivergence of at least 2000 or a little more than five Principal line 1 • oF Rhodium. • • . Diamond (IJ/J • • • • •k * • •• • • ■ • • •• • • • • •* ; • Glancing anale Fig. 7. minutes of arc. The anticathode spot had a certainwidth which further increased the small diverofence.Thus the extent of the range of reflection is largely,if not entirely, accounted for. No want of precisionof the angle of reflection is roade apparent, and thecrystal appears to be almost perfect. THE X-RAY SPECTROMETER 31 The principal objects in view, when choosing amethod of observation, are intensity and sharpness ofdefinition or resolving power. The two are notalways compatible with each other. In consideringthe question, certain geometrical relations are of im-portance, and these we will now consider. Suppose the rays to issue from a point source (^(Fig. 8) which may be the anticathode spot, or the R P T
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Fig. 8. slit at A in the wall of the box. Let the crystal facebe in the position PJ^, P being on the axis of thespectrometer. Let the ray OP be reflected to D, theslit of the ionisation chamber. Let PR be a secondposition of the crystal face, the crystal having beenturned through the angle RPR. Let R be theintersection of PR with a circle through OPD.The angle ORT is equal to the angle ODP, and theano-le PRD to POD. Also ORD - OPD. Conse-quently if OP is made equal to PD, that is to say, ifthe source and the ionisation chamber slit are at thesame distance from the axis of the instrument, theangles made by OR and RD with the positionPRToi the crystal face are the same as those madeby OP and PD with the face in the position PR.If a ray of wave length X is reflected along PD inthe one position of the crystal, it is reflected along 32 THE X-RAY SPECTROMETER RD in the other. The crystal in quite differentpositions reflects the ray to the same point D. Thusthe position of the ionisation cha

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