PRINCIPLES OF RADIOLOGICAL PHYSICS 



101 



1.8 

 1.6 

 1.4 

 1.2 " 



-1.0 



CL 



0.8 y 







0.5 



3.0 



06 

 0.4 

 0.2 

 



1.0 1.5 2.0 2.5 

 ENERGY, Mev 



Fig. 1-61. The extrapolated range Tt^ for electrons of different energies. The upper 

 curve refers to the scales on top and at the left of the diagram ; the lower curve refers 

 to the bottom and the right scales. (Evans, 1948.) 



1.8 



1.6 



1.4 



1.2 



E 



i^ 10 - 



.1 0.8 - 



0.6 - 



0.4 



0.2 - 



0.5 1.0 1.5 2.0 2.5 

 F^, Mev 



3.0 3.5 



Fig. 1-62. The maximum range Rm, in g/cm^ of aluminum, for /3 rays of some 

 radioactive materials with different maximum energies Em. (Evans, 1948.) 



''tail" of the curve, but this tail may fade into the "background" of 

 particles which are scored by the detector even in the absence of the 

 jS-ray source. 



It so happens that the curves of transmission vs. depth have approximately 

 the same shape as the graph of the exponential function e"'' over a fairly extended 

 range of values of the depth. This is confirmed by the fact that the semi- 

 logarithmic plot of the same data (Fig. l-63b) approximates a straight line. 



