26 



BIOPHYSICALLY ACTIVE X-RAYS 



Therapeutically, the back scattering is therefore a decidedly important 

 phenomenon, especially for very hard x-rays, because of the increase in 

 wavelength and its accompanying greater absorption in this direction. 



TABLE 1-6 



Ratio of Intensities of Modified to Unmodified X-Radiation 

 in the Compton Effect 



Source, Ag K line (0.56 A) 

 Observations made at 120° with incident beam 



For additional data see Y. H. Woo [1926]. 

 Courtesy Physical Review. 



The Compton modified scattering varies with the atomic number 

 of the filter or absorber element. Thus for elements of smaller atomic 

 number than lithium all the incident energy is modified and scattered 

 as softer radiation, whereas for lead practically none of it is modified. 

 Table 1-6 due to Y. H. Woo [1926] gives some idea of the importance 

 of the ratio of the intensities of the modified to the unmodified x-radia- 

 tion, especially when tissue and absorbing material of low atomic number 

 are radiated. 



The Translucence oe Human Tissue 



The above discussion on the transmission of x-radiation by matter 

 permits a rather unusual conclusion about matter of low atomic weight: 

 that it is translucent and not transparent to x-radiations. If the human 

 eye were sensitive to x-rays, human tissue, which is composed wholly 

 of elements of low atomic number, would be seen as a bright vaporlike 

 substance if irradiated with x-radiations. An x-ray photograph (radio- 

 graph) of an internal organ of the human body is similar to a photograph 

 of a building taken in a fog: the parts of the building nearer the camera 

 would appear more clearly in the photograph, and the distant parts less 

 clearly or not at all; while the larger outlines would be visible with 



