Subsurface Laboratory Methods 



227 



substances or very simple mixtures, but does not appear to be of much 

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

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

 lines from the different patterns of the constituents in the mixture. Refer- 

 ence to table 8, which shows the angular range of corresponding patterns 



Exposure (intensity x time) 

 Figure 97. Exposure-density curve for typical X-ray film. 



produced by the common target materials available as compared to the 

 full pattern range (170°) for chromium Ka 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 Ka of 



