File:X rays and crystal structure (1915) (14591300980).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

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cted fromthe face itself, though we know really that it is notat the face, but inside the crystal that reflection isoccurring. Yet, since the rays do not usuallypenetrate more than a millimetre in depth into thecrystal, and often much less than a millimetre, it isonly a thin layer parallel to the face which is engagedin the reflection. In future we shall, for brevity,describe a reflection of this kind as reflection by theface. So far we have considered the reflection of a singlepulse. We may now proceed to consider the reflec-tion of a regular train of waves. Each plane reflects * W. L. Bragg, Proc. Camb. Phil. Soc. vol. xvii. part i, p. 43. 16 DIFFU.UTUA i^F WANKS the wave train as a wave train, but when the reflectedtrains are in the s;\me phase, that is to say, are soarrani?ed that thev fit on to each other exactly, crestto crest, and hollow to hollow, the reflected enercvis far greater than if this condition is imj>erfectlyfulfilled, even if the want of tit is exceedinglysmall.
Text Appearing After Image:
Let the crysiai structure be represented in Fig. 3by the series of planes, /, /, /, mon distance ap;irt or * spacing. .-/, ^,, .^j, --Is •-are a train of advancing waves of wave length X.Consider those waves which, after reflection, join inmoving along Bl\ and comj>are the distances whichthey must travel from some line such as A A beforethey reach the point C. The routes by which theytravel are ABC, ABC, ABC and so on. DrawBX ;>erjxMidicular to AB\ Produce AB to />,where D is the imag^ of B in the plane thRUigh B\Since BB^Bll^nd AX^AB, the ditl^r^nceIxnween A/^C and ABC is equal to AY>. that is to >£. ^i*^^. ■- ^*»S- !&&»*: T^ _. ^ ^^ -* ■—v _ :,.., ^j«5rtfet%- IbH.^ 5J.Ji- 18 DIFFRACTION OF WAVES If, therefore, we measure the angles Oj, 0.,, 6.^, atwhich reflection occurs, it gives us a relation between\ the wave length and d, the constant of the grating.By employing the same crystal face, the wave lengthsof different monoch

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