182 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 7 



Table 27. The Natural Radioactive Series and Alpha Particles — {Continued) 



Isotope 



Symbol 



A 



Half-life 



Range, 



cm in 

 air 



Energy, 

 mev 



Velocity 

 3 X 10"> 



cm /sec 



Disinte- 

 gration 

 energy, 

 mev 



Relative 

 intensity 



Neptunium Series* 



Plutonium 



Americium 



Neptunium 



Protactinium 



Uranium 



Thorium 



Radium 



Actinium 



Francium 



Astatine 



Bismuth 



• 



► Polonium • — 



► (Thallium)* — 



Lead i — 



Bismuth 



500 y 

 2.25 X 10« y 



27. 4d 

 1 . 63 X lO' y 



5 X 103 y 



14 d 

 10 d 

 5 m 



2.1 X 10-2 s 

 46 m 



3.2 X 10-6 s 



3.3 h 



Stable 



(8- 



825 

 ~ 5 

 0- 

 801 

 31 

 023 

 86 



8.336 



* Recent data have made it possible to construct a fourth natural radioactive series which has the 

 form (in +1). Its probable members and arrangement are given above as reported by Hageman, F., 

 L. I. Katzin, M. H. Studier, A. Ghiorso, and G. T. Seaborg, Phys. Rev., 72, 253 (1947), and by English, 

 A. C, T. E. Cranshaw, P. Demers, J. A. Harvey, E. P. Hinks, J. V. Jelley, and A. N. May, Phys. Rev., 

 72, 253 (1947). Thallium 209 is the only member that has not been positively identified. The name 

 "Neptunium Series," after the longest lived member, was proposed in accordance with the practice 

 for naming the other three series. 



hitherto missing 4« + 1 series. Additional radioisotopes that may be found 

 should belong to existing series. For example, mass number 4n + 5 would 

 be merely an existing member or a branch of the 4rc + 1 series. 



Figures 50 to 53 show the order and the half4ives of members of the four 

 series. In the scheme used here, alpha decay corresponds to a displacement 

 of two units to the left, whereas beta decay appears as a displacement of 



