556 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



0.05 0.1 



0.3 0.5 



1 3 5 



ACTIVITY, pCi/g 



30 50 



Fig. 10 Distribution of radionuclides in the sediment core collected at station B-2 in 

 1972. 



0.047, which was found in the 18- to 20-cm section. Below this 18- to 20-cm section, the 

 ratios decreased with depth from 0.0108 to 0.0069, whereas above the 18- to 20-cm 

 section, the ratios ranged from 0.0138 to 0.01 13. 



The ordering sequence of the radionuclide concentrations measured in this core varied 

 with depth. Below the 0- to 2-cm section, the order changed from that shown in Fig. 9 to 

 Pu > Eu > Am > Co > Cs > Bi in the 2- to 6-cm region, to Pu > Eu > Am > Co > Bi > 

 Cs in the 6- to 26-cm region, to Co > Pu > Eu > Am > Bi > Cs in the 26- to 38-cm 

 region, and to Pu > Eu > Am > Co > Bi > Cs in the 38- to 40-cm region. 



Station B-20. The distribution of ^^^•^'^^Pu, ^^^ Am, and ' ^^Eu concentrations in this 

 core (Fig. 1 1 and Table 3) was again quite similar and decreased with depth by 50% at 

 about the 9-cm section. At 1 1 cm in the core, a sharp break occurred between the finely 

 divided material in overlying sections to coarse sand. Considering the range and 

 distribution of 2 3 8p^j^2 3 9,2 4 0pu j-^i^jq^ measured in surface sediments across the lagoon, 

 the ratios found in the three sections of this core were uniquely low, which possibly 

 indicates a common sourcef"^) for the majority of the plutonium contamination in the 

 sediment column collected at this station. Only in the 6- to 8-cm section of this core does 

 the radionuclide ordering sequence differ from that found in surface sediments (Fig. 9). 

 In this section the ordering of ^"^ ' Am and ^ ^ ^ Eu concentrations was reversed from those 

 in other sections. This order, Pu > Am > Eu, was found in sediments only in the four 

 sections from the bottom of the Bravo crater core and from the eastern lagoon. 



Bismuth-207 concentrations were below the limit of detection in most sections of the 

 core. However, the concentration of ■^°^Bi in the 0- to 2-cm section was at least four to 

 five times as high as that in any lower section. 



The concentrations of ^ ^Co and ' ^ ''Cs decreased, respectively, to 50% of their largest 

 concentration at the 9- and 11 -cm levels in the core. However, neither of these 



