2g gts . ~~ SO yu BARS Ma rf 730 | Noshkin et al. 2000 mCi/km= Bravo Cratera6, yo17 1000 mci /km? 967_ ao “ 939 Coa2 1772 . é 38 2439 Bikini Atoll. From these data we explain the relative behavior of some specific radionuclides in Bikini Atoll. This work was part of a cooperative program to investigate the biogeochemical behavior of the transuranium elements at Bikini Atoll. Samples were collected in November 1972 from the RV Palumbo, operated by the Puerto Rico Nuclear Center (PRNC). We acknowledge the help provided by the crew of the RV Palumbo and specifically thank F. Lowman and W. Schell, cooperative participating investi- 1-100 mCi /kn2 36 43 100 mCi/km2 228 139 a <1 Fig. 1. Bikini Atoll—location of sampling station and Bravo Crater. Isoactivity lines of **Am (mCi km) in the surface (2.5 cm) sediment of Bikini Lagoon. mation on other possible mechanisms controlling the redistribution of specific radionuclides, principally the transuranium elements. We prepared autoradiographs and Xradiographs from vertical slices cut from the center of a sample of Favites virens collected from Bikini Atoll. Autoradiography revealed three discrete, relatively intense, radioactive bands within the skeletal structure identifiable with the nuclear test series of 1954, 1956, and 1958. Fourteen density bands between the outermost radioactive band (1958) and the coral surface (1972) confirmed the thesis that these are correlated with annual growth. Sections from each annual growth band were analyzed by low-level gamma spectrometry and radiochemical techniques to reconstruct the chronological history of specific radionuclides incorporated in the coral skeleton. Much, if not all, of the observed artificial radioactivity in the coral at Enewetak (Knutson and Buddemeier 1973) was due to Sr and its daughter *°Y, but we identified other radionuclides in all growth sections of this Bikini coral (e.g. 241Am Sr 15ky, 27Bi 8Co, 21°Po, 238, 239.240,241Py)_ We believe that the record recovered in these yearly growth increments is one of the most complete histories of changes in concentration of specific radionuclides in the marine environment of gators. Sectioning methods and growth results The coral used in this study was a live specimen of F. virens dredged in November 1972 from a depth of 28 m at station B-3, Bikini Atoll (Fig. 1). In the periods of June-July 1946, February-May 1954, May-July 1956, and May-July 1958, Bikini Atoll was the site of a series of nuclear device tests. Many of the events in the last three series were conducted along the inner northern and southern perimeter of the lagoon. The largest test on the reef (1954: 15 megatons) (Telegadas 1961) produced Bravo Crater, also shown in Fig. 1. Table 1. Concentration of “Am, “Eu, “Co, and *”Bi in the sediment column from location B-3; water depth, 28.3 m; collection date, 8 November 1972: core diameter, 36.3 cm’. Section Thickness (om) pCi/g dry + (error in % of value)” aul 1555) 60n9 “207, 5 Coarse fraction > 0.5 mm 0-5 5-10 10-15 15-20 20-25 25-30 30-35 T.1043 5.1743 9.2242 6.1342 3.484h 4.o2sh 1.16410 2,64+6 2.4145 0.89410 < O.1 < 0.1 2.6644 1.1944 0.15424 0.13430 1.7146 O.67+9 0.29418 0.20425 2.744h 0.9645 0.39416 0.38416 5.9323 7.OL#L 3.8946 3,.674h Fine fraction < 0.5 mm 0-5 5-10 10-15 15-20 8.3742 11.1 +2 20.3 +2 15.7 +2 25-30 30-35 1.7346 1.5846 20-25 8.2643 13.4 44.8 22.4 17.3 41 42 42 +2 8.7322 2.09th 1.8944 5.0642 6.8343 7.4543 4.7845 2.0026 0.8949 0.60412 *Based on counting error only. . t tS ‘SOF .sRCTINE 1.3848 2.3146 11.82+2 12.4143 3.6245 1.1448 0.68410