On D+4 the second sample (Method II) was placed in a vessel containing 75 ml of sea water. After stirring for a certain time interval, the solution was centrifuged and a 50-) aliquot re- moved from the supernate. This procedure was repeated several times over a 48-hour period, with the activity of each fraction being measured shortly after separation and used to compute the cumulative percent of the total activity in solution (Figure 3.11). The gamma spectrum of the solution stirred for 48 hours was also measured for comparison with the spectra obtained by Method I (Figure 3.12). As indicated in Figure 3.11, more than 1 percent of the total activity went into solution in less than 10 seconds, followed by at least an additional 19 percent before equilibrium was achieved. This was accompanied by large spectral changes, indicating marked radionuclide fractionation (Figure 3.12); nearly all of the '3!, for example, appears to have been dissolved in 360 seconds. The dip-counter activities of all water samples taken by Projects 2.63 and 2.62a are tabulated in Table B.32. Ocean background corrections have not been attempted but may be estimated for each shot at the YAG 39 and YAG 40 locations from the activities of the background samples collected just prior to the arrival of fallout. All other corrections have been made, however, including those required by the dilution of the designated 1,100-ml depth samples to the standard 2,000-ml counting volume. Normalized dip-counter decay curves for each event (Figure B.14), and the records of the surface-monitoring devices (NYO-M, Figures B.8 through B.13) are also included in Section B.4. 3.3. PHYSICAL, CHEMICAL, AND RADIOCHEMICAL CHARACTERISTICS 3.3.1 Solid Particles. All of the active fallout collected during Shot Zuni, and nearly ali collected during Shot Tewa, consisted of solid particles which closely resembled those from Shot M during Operation Ivy and Shot 1 during Operation Castle (References 21 and 22). Alter- nate trays containing greased disks for solid-particle collection and reagent films for slurryparticle collection were used in the IC’s during Shot Tewa. Microscopic examination of the latter revealed an insignificant number of slurry particles; these results are summarized in Table B.10. No slurry particles were observed in the Zuni fallout, although a small number May have been deposited. As illustrated in Figure 3.13, the particles varied from unchanged irregular grains of coral Sand to completely altered spheroidal particles or flaky agglomerates, and in a numberof cases included dense black spheres (Reference 19). Each of these types is covered in the discussion of physical, chemical, radiochemical, and radiation characteristics which follows. Basic data for about 100 particles from each shot, selected at random from among those removed from the SIC trays in the YAG 40 laboratory, are included in Table B.34. Physical and Chemical Characteristics. A numberof irregular and spheroidal Particles collected on the YFNB 29 during Shots Zuni and Tewa were thin-sectioned and studied under a petrographic microscope (Reference 23); some from Shot Zuni were also subjected to X-ray diffraction analysis (Table 3.7). Typical thin sections of both types of particles are preSented in Figures 3.14, 3.15 and 3.16 for Shot Zuni and Figures 3.17 and 3.18 for Shot Tewa. Although the particles shown in the figures were taken from samples of close-in fallout, those Collected 40 miles or more from the shot point by the SIC on the YAG 40 were observed to be ‘Similar, except for being smaller in size. Both methods of analysis showed the great majority of irregular particles to consist of fine- rained calcium hydroxide, Ca(OH),, with a thin surface layer of calcium carbonate, CaCO, (Figure 3.17). A few, however, had surface layers of calcium hydroxide with central cores of Unchanged coral (CaCO), and an even smaller number were composedentirely of unchanged Coral (Figure 3.14). It is likely that the chemically changed particles were formed by decar- bonation of the original calcium carbonate to calcium oxide followed by hydration to calcium hydroxide and subsequent reaction with CO, in the atmosphere to form a thin coat of calcium Carbonate. Particles of this kind were angular in appearance and unusually white in color (Fig- Ure 3.13, A and G). Many of the irregular particles from Shot Zuni were observed to carry small highly active 49