156 



TSOTOPIC TRACERS AND NUCLEAR RADIATIONS 



[Chap. 6 



Table 22. Transmission and Stopping Power of Various Substances for Fission 



Fragments [37] 

 The upper number of each pair is the foil thickness in milligrams per square centimeter 

 necessary to stop a given fraction of fragments. The lower number is the stopping power 

 relative to aluminum. Some error was introduced by the method of detection, and the 

 second set of absorber thickness for the end point, in parentheses, is corrected for 0.8 mg per 

 cm 2 of aluminum to give what is estimated to be the true end point. 



fragments are enabled by these radioactive chains to terminate in known 

 stable isotopic species. An example of a typical chain is that following from 

 the initial fission fragment 52 Te 135 [12]: 



54 Xe 135 — 3m 



/ \ 



52 Te t35 — 2w -> 53I 135 — 6.7 55 Cs 135 — 2.5 X 10 4 y -> 56 Ba 135 



\ / 



54 Xe 135 — 9.2h 



(stable) 



A few of the many possible initial fission fragments are known to be stable, 

 whereas others decay by the emission of as many as six successive beta 

 particles. On the average each fragment undergoes three beta transforma- 

 tions accompanied by its characteristic isomeric transitions. Many of the 



