TRANSURANIC RADIONUCLIDES IN ENEWETAK LAGOON 583 



^^^Pu and ^"^^Pu activities as has so often been done in the literature. Throughout this 

 report, '^^ ^"^^Pu will refer to the sum of the activities of the two radionuclides, and 

 ^^^Pu will refer to only that isotope. 



In two Enewetak lagoon water samples collected during 1972 (Noshkin, 1974), 

 ^'*' Pu was measured by mass spectrometry. The ^^'Pu/'^^^ ^"^^Pu activity ratios as of 

 December 1972 were 1.14 and 2.56. hi the 1972 growth section of the previously 

 mentioned live coral from Bikini, the ^'^'Pu/'^'^^ ^''^Pu activity ratio was 11.7 and the 

 24ip^^239p^ ratio was 21.0 ±1.1 (Noslikin et al., 1975). As of Jan.l, 1975, the 

 ^"^^Pu/^^^Pu ratio in soil samples from Bikini and Eneu islands and in Bikini Island 

 vegetation averaged 22.0 ±3.3 (Mount et al., 1976). Correcting the ^'*^Pu in the 

 November 1972 coral growth section for decay to Jan. 1, 1975, yields a ■^ "* ' Pu/^ ^ ^ Pu 

 ratio of 18.9 ±1.1. Bikini and Eneu islands and the sedimentary environment from which 

 the coral was obtained were contaminated principally with radioactive debris from the 

 1954 Bravo event. The good agreement between the ratios determined in the terrestrial 

 and marine samples indicates a lack of discrimination between ■^'^^ Pu and ^ ^^Pu isotopes 

 in processes in these environments. Bikini and Enewetak have very different isotopic 

 ratios and therefore different inventories of plutonium isotopes. The amount of ^ "* ^ Pu in 

 the environment regulates the projected inventory of ^^' Am through growth and beta 

 decay of the parent radionuclide. The amount of ^^' Am that will be generated at Bikini 

 from ^^' Pu decay will exceed the amount produced by this source at Enewetak. 



Americium 



The distribution of ^"^^ Am is also wide spread in the aquatic environment of the Atoll. 

 Although the highest concentrations of plutonium and americium are in the same areas of 

 the lagoon at Enewetak, the two transuranics are distributed differently. The ^"^^ Am/ 

 239 240p^ j.^^-Q jj^ sediments collected from the lagoon during 1972 ranged from 0.06 to 

 0.93. Signitlcant errors, therefore, can be introduced if one transuranic is used to predict 

 the levels of others at any given location in the lagoon. No other americium isotopes were 

 detected in the aquatic environment of either Enewetak or Bikini. 



Curium 



No strenuous effort has been made to obtain an inventory of ^'*'^Cm or ■^'''^Cm in 

 Enewetak by alpha spectrometry. Curium activities were separated and measured in 

 several lagoon water samples: ^"^"^Cm activities were less than 0.2 fCi/liter. No ^'^'^Cm or 

 ^"^"^Cm was detected in sediment samples from the Bravo crater at Bikini Atoll (Beasley, 

 1976). 



Higher Transuranic Elements 



No information is available to my knowledge on either berkelium or californium in 

 marine samples from Enewetak or Bikini. 



Transuranic Elements in the Benthic Environment of Enewetak Atoll 



Surface-Sediment Distributions and Inventories 



The distributions of ^^^"^^"^^Pu and ^'^^ Am activities measured in December 1972 in the 

 2.5-cm-thick surface layer of sediment from the lagoon floor are shown in Figs. 2 and 3, 



