112 



RADIATION BIOLOGY 



Figure 1-72 gives data on the energy dissipation as a function of depth for 

 X-ray beams of various energies penetrating various materials. As the energy 

 increases the curves take progressively the appearance of the curves of energy 



1600 



~ 1400 



o 



I. 



o 



1200 



1000 



800 



Et 600 





>- 

 o 



400 



200 











10 



30 



35 



40 



15 20 25 



DEPTH, cm 

 Fig. 1-72. Energy dissipation at various depths within a Presdwood phantom by 

 X-ray beams of a betatron operated at different energies. {Charleton and Breed, 

 1948.) 



dissipation by cascade showers in Fig. 1-58. In fact, a shower develops essen- 

 tially in the same way whether it is initiated by an X-ray photon or by an electron 

 of equal energy. 



COLLIMATED AND COMPENSATED BEAM 



HORIZONTAL MEDIAN PLANE ■ ■ 



2 4 6 8 10 12 14 



DEPTH, cm 

 Fig. 1-73. Energy dissipation in various portions of the X-ray beam from a 20-Mev 

 betatron as it passes through a Presdwood phantom. The beam has been passed 

 through a compensating filter which sharpens its edges. {Adams et al., 1948.) 



The travel of electrons contributes also to the distribution of energy sidewise 

 from an X-ray beam. Figure 1-73 gives some illustrative maps of the energy dis- 

 sipation prcxluced by beams of high-energy X rays. 



