220 Subsurface Geologic Methods 



adopting a sample holder capable of rotating the sample at a rate which 

 would average out the orientation effects. 



The Geiger-Mueller-counter apparatus is especially recommended by 

 the manufacturers for quantitative analytic work. The observations stated 

 above, however, would introduce some question concerning this applica- 

 tion. Furthermore, other research groups have found the apparatus unsuit- 

 able for quantitative analytic work, especially when used with recorder 

 apparatus.^* 



Conflicting statements concerning operating characteristics of Geiger- 

 counter apparatus have also been made.^^ ^® 



It has been pointed out by Friedman ^^ that a microphotometer trace 

 of a film pattern made with a conventional diffraction camera has so 

 much intensity variation in the background that it is difl&cult to detect 

 low-intensity lines in the pattern. However, inspection of the curve shown 

 indicates that most of this variation was due to improper adjustment of 

 the microphotometer on which the trace was made. Furthermore, this 

 same paper also shows a comparable curve obtained with a Geiger-counter 

 apparatus. The curve obtained with this apparatus has a uniform back- 

 ground intensity as compared to the gradually diminishing (with larger 

 Bragg angle) background intensity always obtained in microphotometer 

 traces of film patterns made with diffraction cameras. The writer has ob- 

 tained similar curves with a Geiger-counter apparatus furnished with a 

 single defining slit producing a divergent X-ray beam. It was soon ob- 

 served that at lower angles part of the X-ray beam spilled over at the ends 

 of reasonably short samples commonly used, thus causing the uniform 

 background (See b of fig. 94). On the other hand, a sample 16 cm. long 

 gave a curve very similar in background intensity to microphotometer 

 traces obtained from film patterns. Owing to the geometric shape of this 

 sample and the setup of the apparatus, not all of the diffracted rays were 

 gathered into the counter tube through the small slit directly in front of 

 the counter tube. An even steeper background curve should have been ob- 

 tained if the setup had been geometrically that of the focusing camera. 

 Consequently, all lines recorded at lower angles must obviously have been 

 abnormally weaker than they should have been if no part of the X-ray 

 beam had spilled over at the ends of the sample. The amount of beam 

 spillover was a function of the length of the sample and of the magnitude 

 of the Bragg angle and was of considerable importance for the short sam- 

 ples (2 to 3 cm. long) usually recommended. 



^* Klug, H. P., Alexander, L., and Kuramer, Elizabeth, Quantitative Analysis with the X-ray Spec- 

 trometer: Anal. Chemistry, vol. 20, pp. 607 ff., 1948. 



^^ Carl, H. F., Quantitative Mineral Analysis with a Recording Diffraction Spectrometer: Am. Mineral- 

 ogist, vol. 32, pp. 508 ff., 1947. 



^° Lonsdale, Kathleen, Note on Quantitative Analysis by X-ray Diffraction Methods : Am. Mineralogist, 

 vol. 33, pp. 90 fif., 1948. 



■"Friedman, H., Geiger-Counter Spectrometer for Industrial Research: Electronics, vol. 18, pp. 132 

 ff., 1945. 



