128 



MICROSCOPIC TECHNIQUES 



The use of the roentgen absorption method requires an under- 

 standing of the theoretical basis of roentgen spectroscopy. All that 

 can be included here are a few of the more salient features of the 

 theoretical treatment which Engstrom ( 1946, pages 19-50) applied 

 to his method, a description of the apparatus, and consideration of 

 certain other practical aspects. This information can serve merely to 

 acquaint the reader with the method, the actual use of which will 

 depend on the understanding of roentgen spectroscopy mentioned 

 l)reviously and a detailed study of the presentation of Engstrom 

 (1946). 



WAVE LENGTH 



Fig. 15. Schematic representation of an absorption jump. 

 From Engstrom (1946) 



1. Some Theoretical Aspects 



Quantitative analysis based on the roentgen absorption utilizes 

 the absorption discontinuities which appear at a characteristic 

 wavelength for every element. The absorption of an element near 

 the K-absorption edge is indicated in Figure 15. The determination 

 of the element depends on the measurement of the absorption of 

 monochromatic radiation wnth wavelengths on each side of, and 

 close to, the absorption edge of the element to be determined. 



The mass (x), in g./cm.^, of the element to be analyzed is given by 

 the following equation: 



In 



X = 



A 



Ml 

 P 



(S)' 



In 



M2 

 P 



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