990 



EXPLORATION GEOPHYSICS 



MASS NUMBER 



Fig. 605. — The natural radioactive series. (After R. D. Evans, The Science and Engineering of 

 Nuclear Power, Vol. I, Addison-Wesley, 1947). 



Mev. The range of the average energetic a in aluminum is of the order of 

 10"^ cm. 



There is much greater variety in the energy (Emax) of known natural 

 beta emitters, with a distribution from a few Kev to 3.1 Mev (Bi^'^^ in 

 the U series). But a beam of Yi Mev ^'s will be stopped almost completely 

 by a 16-gauge sheet of aluminum. 



Natural gamma-rays have energies up to 2.2 Mev. Energetic ("hard") 



