sparrow: cytogenetic effects of ionizing radiations 



61 



at a particular position below the surface is called the depth dose 

 and is determined by a large number of factors, including such things 

 as kind and energy of radiation (Figure 2), size of the area irradiated, 

 chemical composition and density of the specimen or tissue, collima- 



100 



h 



80 



60 



I 



^ ¥0 



20 



15 



20 



cm 



5 10 



Depth in plastic 



Figure 2. — Comparison of the depth dose effect between deuterons and 

 electrons. Curve taken from Tobias, Anger, and Lawrence (189). These 

 curves were determined experimentally, using a plastic having an absorp- 

 tion coefficient similar to tissue. 



tion of the beam, etc. These factors are generally thoroughly discussed 

 in books on radiological physics or radiation therapy (10, 51, 52, 76, 

 113, for example). These should be consulted for further detail. 



Another important characteristic is the relative density of ioni- 

 zations along the path of the ionizing particle. (See Figure 14.) As 

 can be seen from Table 2, this varies widely for the different radi- 

 ations, beginning at a minimum of approximately 8 ionizations per 



