‘Weha Raa iMlNM es Transuranics in Bikini Lagoon Table 2. 733 growth band; at least 1 mm of material Coral section data. waslost at each cut, so that the coral recsection from outer edge Estimated Amm At in years year {collection date) year of égrowth/ 1971-1972 1970 1969 1968 1967 1966 1965 4 7 6 8 9 8 10 1963 1962 1961 1960 1959 1958 10 8 13 12 8 T 9.4 10.4 11.4 12.4 13.4 1h.k 8 5 9 16.4 1T.9 18.4 growth from Nov 72 (mm) 0-8 8-15 - 15-21 21-29 29-38 38-6 46-56 56-65 65-T5 75-83 83-96 96-108 108-116 116-123 123-129 129-137 137-L47 L47-156 ies (not all necessar‘or radionuclide anal- wever, is only 2.5 rowth rate during yr, The annual ‘constant thickness; oundaries to postthe density variaay film. :posed X-ray film reful examination ind dark bandsin al exposures were dlete selection of ” could be made. 1974) concluded ind (dark X-ray ith a growth peecember or Januly. In our sample, tutoradiograph of 1964 1957 1956 1954-1955 1953 9 6 0.9 2.4 3.4 uk 5.4 6.4 7.4 Buh 15.4 the Bikini coral are either associated with the low-density bands of the X-ray negative or close to the transition zone between light and dark bands. By correlation of the bands shown by both the autoradiograph and X-ray exposures, the years 1956 through 1958 were identified. The 1954 growth, however, could not be resolved from the 1955 growth on the X-ray negative. From the 1958 bandto the coral surface (1972 growth), 14 alternating light and dark areas were identified (Fig. 3). Table 2 gives the thickness of each annual section along with the estimated year of growth. The varying dimensions of the yearly increments show that growth rates vary from year to year and also that the dimensions follow no predictable trend with time. The mean annual growth from the X-radiograph is 8.1 +2.2 mm yr, a value in agreement with the autoradiography results. No activity from the 1946 test was detected because it predated the earliest growth of this particular coral. A wedge, containing the area with the more nearly linear growth record, was removed from the center of the slice (see wedge outline, Fig. 3). A bandsaw was used to remove each defined annual ord between each two sections was lost. Each section was then ground and homogenized in a ball mill and a known weight was transferred to a vial for radionuclide analysis by gamma spectrometry. A low-background, Compton-suppressed, Ge(Li) detector system was used for some of the gamma-emitting radionuclides. The samples were then processed for Pu, *Sr, and 210P9 by chemical separation followed by radioassay with low-background beta detectors and alpha spectrometry. Selected samples were also analyzed by mass spec- trometry to determine 74°Pu,.?3°Pu, and 241Pu. The analytical techniques were essentially those described by Wong (1971) and Noshkin and Gatrousis (1974). Stable strontium was determined by atomic absorption. Our discussion here will concentrate primarily on the transuranium elements; however, Tables 3-5 give the results for all the radionuclides analyzed, expressed as pCi g! (dry wt) and corrected for decay back to the estimated year of growth. Two sources contribute to the ?4Am levels found in the coral. Part is from the radioactive decay of the parent radionuclide *41Pu, while the remainder is unsupported 2414m. Based on the quantities of 244Am and 74!Py, the time between separation, and the age of the coral section, levels of both supported and unsupported *#4Am are computed and given in Table 5. Radionuclide results General—The coral bands identified with the 1954, 1956, and 1958 test series, as would be expected from the autoradiograph, contain the highest concentrations of radionuclides. A spectrum from 12 g of the 1954 growth section is shown in Fig. 4 with each prominent gammaray identified. Severai gamma-emitting radionuclides with half-lives less than 1-2 years have been identified in earlier surveys (Welander 1969); these were not detected in any coral sections with our spectrometer system. Other radionuclides requiring radiochemi- 4. Growth