Subsurface Laboratory Methods 



217 



radiation wave lengths to spread out the patterns and increase the resolu- 

 tion should increase the number considerably. The most important disad- 

 vantages of the method are its inability to detect amorphous phases, such 

 as glasses, when present in only limited amounts, and the fact that solid 

 solutions may not always be observed. 



Apparatus for Recording the Diffraction Patterns 



Two general types of apparatus are commonly used for recording 

 the X-ray-diffraction pattern. Both are essentially the same in regard to 

 the generation of X-rays, being composed of a high-potentional (30,000 to 



Focal spot on 

 torget of 

 X-ray tube 



Focal spot on 

 torget of 

 X-ray tube 



Sample 



,, \ ^^ X Counter/ 

 V \ "-^-^.slit- 



-Counter tube 



/ 1000- 1400 Volts 



y Poth of counter 

 ^ / tube 



Figure 94. (a) Schematic diagram of focusing powder camera, (b) Schematic dia- 

 gram of relation of focusing camera to Geiger-Mueller-counter apparatus. 



50,000 volts) source of current, including a line voltage stabilizer, an 

 auto-transformer to regulate the high potential, the necessary controls, 

 rectifier, and X-ray tubes. The difference in these types of apparatus 

 arises in the manner in which the X-ray-diffraction patterns are recorded; 

 one type uses the conventional diffraction camera with photographic 

 film and the other, a Geiger-Mueller-counter tube with a scaling circuit 

 that may be used to measure the intensity of the diffracted rays, records 

 intensity either by the counting technique or by automatic recording ap- 

 paratus. The conventionl camera is shown schematically in figure 93. 



