RADIOACTIVE ELEMENTS AND DEEP-SEA SEDIMENTS 



371 



the three radioactive famihes have isotopes of the same element 

 at their head: U-^^ and U-'^\ It is possible, in such cases, to calcu- 

 late the age of the system by applying one of the methods described 

 above, when only the ratio of the concentrations of two members 

 of the two families, independently of the absolute value of their 

 concentrations is known. We shall cite an example of this type 

 later. 



The Serviceable Radionuclides 



The curves in Figs. 1 and 2 show that, in order to date a par- 

 1 



N/No 



Be 10 (2,7- 10 y) 



0,5 



0,1 - 



0.05 ] \ci^(5,51 

 0.005 



time(x lOycars) 



Fig. 2. Decay curves of radioactive nuclides used for dating pelagic sediments 

 (back to '^ W years). 



