PENETRATION OF THE RAYS INTO TISSUE 



117 



2 2 



c 



<u c 

 ■o — 

 'o .c 



^_ 0) 

 O T3 



c a> 

 o c 

 "*- !c 



O o 



o □ 



alphas 



(0 001 mm) 



(7 mm 



(I mm) 



gam mas 



or 

 neu t rons 



(several 

 feet) 



Depth in tissue 

 Figure 5-9. Penetration of 1 Mev Alphas, Betas, Gammas, and Neutrons into tissue 



In simplest cases, the curve for gammas is truly exponential; that for betas 

 has less curvature and reaches a maximum value, which is the depth of 

 penetration of the fastest betas. Note that the area under each curve corre- 

 sponds to 100 per cent of the impinging rays hitting the target. The depth of 

 penetration is radically different for the three cases. 



TABLE 5-3. Ranges of Various Types of Radiation in Soft Tissue.* 



*Krom "Radiological Health] [andbook," National Bureau of Standards Wa hington, D. C, I960 



**Range for absorption of half the incident radiation. 



***From "Safe Handling of Radioisotopes," Health Physics Addendum," < G Vppleton and I' N 

 Krishnamoorthy. Eds., International Atomic Energy Agency, Vienna, I960 



+From G. J. Hine and G. L. Brownell. "Radiation Dosimetry," Academii Press, [n< 1956 and W 

 Whaling, "The Energy Loss of Charged Particles in Mattel " Handbuch der Physik, XXXI\ 



