TRANSURANIC ELEMENTS AT BIKINI ATOLL 555 



6i > Pu - Eu > Co > Am > Cs 



A Pu Am ' Eu 

 • Eu ■ Pu ■ Am 

 ■ Pu > Eu ;. Am 



\0.039' VSl^~i'~ 



Co > Bi > Cs 



Pu Eu - Co ■ Cs - Am > B 



Co ■ Pu > Eu > Am > Bi > Cs 



Fig. 9 Distribution of the ordering sequence of radionuclide concentrations in the 

 surface sediments of Bikini AtoU lagoon. The ^ ' * Pu/^ 3 « .2 4 o p^ ratios at each station for 

 the year 1972 are also shown. 



Station B-2. The distribution of "^'^''^Pu, ^^ ^ Am, ^^''Bi/ ^^Eu, ' ^ v^.^^ ^^ eo^.^ ^ 

 the sediment core collected at station B-2 is shown in Fig. 10, and that of ^"^^Am, 

 2 3 9,2 4 0p|j^ 2 3 8py^ ^^^ ^^ ^Po is shown in Table 3. Several features of this long core were 

 similar to features in other sediment cores collected from the northwest quadrant. The 

 sediments in this core consisted of mixtures of Halimeda and pulverized fine coral 

 material; Halimeda predominated at the 8- to 10-cm section. The distribution of ^^ ^ Am, 

 2 3 9,240p^^ 1 5 5£u^ ^^^ ^ '^ ''Cs Concentrations at station B-2 was similar to that at station 

 B-20 except that (1) the absolute concentrations of ' ^ ^Cs measured were lower than the 

 ^"^^Am and '^^Eu concentrations by a factor of 10 and (2) the 2 3 9,240p^ concentra- 

 tions measured were slightly more irregular with depth than the concentrations measured 

 for ^^' Am or ^^^Eu. In the top 11 cm of the core, the concentrations of ^^^'■^^^Pu, 

 ^^*Am, '^"^Eu, and ^^''Cs decreased regularly with depth to 50% of their respective 

 concentrations, which were measured in the surface layer. In the 12- to 26-cm region of 

 the core, the concentrations of ^^^'^"^^Pu, ^'^^ Am, ^ ^^Eu, and ^^''Cs decreased nearly 

 logarithmically with depth. In the 28- to 38-cm region of the core, the concentrations 

 again decreased slowly with depth. 



The distribution of ^^Co and ^^^Bi concentrations in the core was unusual in that 

 decreasing concentrations (with increasing depth) were not found in the upper 10 cm of 

 the sediment core. Although the concentration of ^^Co was relatively constant in the 

 upper 12 cm of the core, the concentration of ^^^Bi increased 50% between the 2- to 4- 

 and 8- to 10-cm sections. Below the 8- to 10-cm section in the core, the decrease in 

 concentrafion of ^'^'^Bi was similar to that of ^"^^ Am, ^ ^^Eu, and ^^''Cs; however, the 

 concentration of ^°Co was almost constant with depth. The distribution of ^^^Pu/ 

 2 3 9,2 4 Op^ ratios measured in different sections of the core was separated by the value of 



