File:X rays and crystal structure (1915) (14775727234).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

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
eries. This division of the planes into two sets willinevitably betray itself in the intensities of thespots ; it will no longer be true that all the spotsform a regular series, but every odd spot will belongto one series, every even spot to another. There-fore, conversely, if we notice this peculiarity in thespots, we are led to imagine the structure of Fig. 72as the cause of it. This is the kind of information which the Lauephotographs give concerning the crystal structure.We consider the spots in the photograph whichcorrespond to reflection in a series of planes of thecrystal such as the series (..I) (211) (311) (411) (.21) (221) (321) (■31) (231) (331) (HI) In some cases th ese spots show perfect regularity 214 ANALYSIS OF LAUE PHOTOGRAPHS as regards their intensity. In other cases the spotswith wholly odd indices, such as (311), (531) ^^^ ^set apart from the others, exhibiting regularityamong themselves, while the rest also exhibitregularity when odd spots are not regarded. Yet
Text Appearing After Image:
Fig. 73. again, there are crystals for which the spots aredivided into three sets : firstly, those with whollyodd indices ; secondly, the spots with one even indexand two odd indices (141) ; thirdly, the set with twoeven indices and one odd index (041), (241). Ineach case the corresponding crystal structure can bededuced. ANALYSIS OF LAUE PHOTOGRAPHS 215 When the whole series of spots shows regularityit corresponds to a crystal structure which has atomsat every point of a simple cubic lattice, just as theregularity in the two-dimensional example corre-sponded to an arrangement of identical points insquares. Fig. )2) shows diagrammatically the photo-graph yielded by potassium chloride, the spots onthe actual photograph being represented in thediagram as dots of corresponding magnitude. Theindices of the planes, in which the spots are reflected,are marked on the diagram. We have already seenthat potassium chloride is for our purpose a perfectsimple cubic lattice, and we now see the abso

Note About Images