17 _ And, at the same time, the difference in 60 Co content between the goatfish from near the crater and those at Bikini I. is by a factor of about ten. . : . . 207_. . It appears that the physical redistribution of Bi is ss 60 Similar to that of oo Co, but since the levels of 207_. Bi are lower than those of 6006 by a factor of about 20, we are at the limits of detection, with the method used, from the crater. for samples distant The use of larger samples, chemical separation and more sensitive counting methods would make it possible to . determine 60 Co: 207_, . . . Bi ratios in sediments, lagoon water and organisms in different parts of the lagoon. These ratios would indicate whether transported radionuclides were primarily in solution or on particles. If the ratios remained constant, that would be a strong indication of transport on particles. results of analyses of selected samples for The 207_., . BL by gamma-ray- spectrometry and by chemical separation are compared in Table 13. Bismuth-207 will be a useful tracer in the future because it has a long half-life, 30 years compared to 5:2 years for 60C0. Plutonium-239, with a half-life in excess of 24,000 years, is another potentially useful tracer. The samplesanalyzed for plutonium were selected on the bases of collection location and content of gamma-emitting radionuclides, which indicate