Sec. 7.11] 



RADIOACTIVITY 



179 



MsTh 



■Th 



2 32 



6.7 y 



MsTh, 



ThB 



ThA 



•Tn 



6.13 h 

 224 224 



ThX RdTh 



1.90 i 



206 



ThC" -^ ThC 



3.i m 



60 6 m, 66 % 



A* 



ThD 



■ThC' 



81 82 83 84 85 86 87 88 89 90 

 ATOMIC NUMBER 



Fig. 52. Thorium series. 



Pu 

 \ 



A/tO y 



241 



209 213 



Tl Bi 



\ 46 m 



\ 



2.2 m^ 



\ 

 \ 



■At 



Pb 



3.3 h 



209 



3.2 xio" 6 : 



Po 



Pa 



2 7.4 d 



Np 



225X10 y 500 y 



Ra 



14 d 



Th 



5000 y 1.65X10 y 



Fa 



Ac 



io d 



Am 



STABLE Qj 



81 8 2 83 84 85 86 87 88 89 90 91 92 93 94 95 



ATOMIC NUMBER 



Fig. 53. Neptunium series. 



, the number of independent series that can be expected to exist. It is seen 

 from Figs. 50, 51, and 52, that the mass number of each member of the 

 uranium-radium series is represented by 4w + 2, where n is an integer. 

 Similarly, the members of the other two natural series are represented by 

 4w + 3 and 4n, respectively. The new series, it is seen from Fig. 53, is the 



