fications, the fast films are preferred, whereas slower films are used if all possible 

 information is to be gleaned from the pattern. Films as a rule are duplitized, 

 that is, they have emulsions on both sides. To a slight extent, the double emulsion 

 causes diffuseness in the lines, but rarely sufficiently to justify use of single-layer- 

 emulsion film. All films should be developed according to the time, temperature, 

 and processing conditions recommended by the manufacturer. 



Intensifying screens have been used for cutting down exposure time, but 

 this practice is not recommended for mixtures of minerals because the screens 

 broaden the pattern lines and thereby decrease resolution. 



The use of the Koz doublet radiation from molybdenum has been recom- 

 mended for chemical analysis by the X-ray-diffraction or Hanawalt method 

 (E43-42T, 1924). This radiation is very good for the identification of metals or 

 alloys which usually have very simple patterns but does not appear to be of 

 much value for complex mixtures such as rocks and soils, for which the 



TABLE 9-1 



Angular Range of Corresponding Patterns Produced 

 By Common Target Materials 



patterns should be spread out as much as possible to prevent superposition of 

 lines from the different patterns of the constituents in the mixture. Reference 

 to Table 9-1 which shows the angular range of corresponding patterns produced 

 by the common target materials available as compared to the full pattern 

 range (170°) for chromium Kcc radiation, should remove any doubt concerning 

 the foregoing statement. The results given in this table should enable the 

 operator to choose the radiation for his particular needs. Where the operator 

 is restricted to a single type of radiation, the Koz of copper is chosen almost 

 invariably because it favorably combines sample penetration with a reasonably 

 expanded pattern of good quality. 



Since the K X-ray spectrum always contains characteristic radiation of 

 several wave lengths, suitable filters (Clark, 1955; Bunn, 1946) or a crystal 

 monochromator should be employed to produce reasonably monochomatic 

 radiation and thus avoid superposition of lines from a second pattern derived 

 from K/3 radiation. In patterns of pure substances or very simple mixtures, the 



161 



