Subsurface Laboratory Methods 



219 



were taken at 15-degree intervals and several counts for each step were 

 taken (to obtain an average value) with the counting technique through 

 the peak of the strongest line in the pattern. The resulting intensity varia- 

 tion is roughly shown in figure 95. The maximum variation observed for 

 the strongest line of the pattern was found to be approximately 60 per- 

 cent when the average mean intensity was used as a basis for the calcula- 

 tion. Naturally, this procedure will give considerably more variation in 

 intensity than will be observed among a group of samples that have all 

 been prepared in essentially the same manner in the conventional type of 

 sample holder. This difficulty of intensity variation might be overcome by 



100% 



90 



180 



270 



360 



Rotation of sample in degrees 



Figure 95. Variation of line intensity with rotation of powder sample obtained 

 with a Geiger-counter instrument. 



