TRANSURANIC ELEMENTS AT BIKINI ATOLL 551 



239, 240 r 



60 80 



ACTIVITY, pCi/g 



Fig. 1 1 Distribution of radionuclides in the sediment core collected at station B-20 in 



1972. 



radionuclides showed steadily decreasing concentrations in the upper layers. The 

 concentration of ^*^Co in the 0- to 2-cm section of the core was significantly lower than 

 that in lower sections. The concentration of '^^Cs at the 0- to 9-cm level of the core 

 showed no appreciable change with depth. 



Station B-21. The concentration profiles of all the radionuclides measured in this 

 sediment core are rouglily similar to those in station B-20 in that the concentrations 

 increased to a maximum at between 5 and 7 cm (except at 3 to 5 cm for ^'*' Am) and 

 then decreased to 50% of their highest measured concentrations at depths of 10 cm, after 

 which increasing proportions of Halimeda began to appear. As in the B-2 core, increased 

 concentrations of radionuclide distributions were measured in the lowest section of this 

 core. As in both of the other cores from this region of the lagoon, the 2 3 8p^^23 9,2 40p^j 

 ratios measured with depth in the core (Table 3) showed only a slight decrease with 

 depth. 



In the 8- to 16-cm region of the core, the ordering sequence of radionuclide 

 concentrations changed from those found in surface sediments (Fig. 9) to the order Pu > 

 Eu > Am > Co > Bi > Cs. This sequence was the same as that observed below the 6-cm 

 section at station B-2 and in surface sediments at the far western region of the Atoll. 



