——me Sample 1 my Sample 2 Sample 3 16% 82% 964 98g Soluble activity in ionic form 23% 8% LS 2% Trace Trace Trace Activity remaining in the insoluble residue Activity in colloidal form 1g Sample 4 The percentages refer to the comparative counting rates of each fraction a3 measured with an end-window GM tube under the same geometrica) conditions, These results are consistent with those found in similar studies cn fallout performed at the site (see Tables 3.5 and 3.6), Sample _}] was obtained from a DMT filter. The sample was leached in water for 3 days and was 20 days old at the beginning of the experiment. Sample 2 was obtained from a DMT filter, The sample was leached in water for 4 weeks and was 25 days old at the beginning of the experiment, Sample 4 consisted of sevaral fallout particles obtained from a belt sampler.<?/ The sample was leached in water for 2 weeks and was 6 1/2 months old at the beginning of the experiment, Sample 4 consisted of several fallout particles obtained from a belt sampler, The sample was leached in water for 3 weeks and was 6 1/2 months old at the beginning of the oxperiment, 4.3.4 Mechanism of Formation The processes by which the fallout particles originated can be described as follows. The material constituting the non-active body of the fallout particle was derived from the coral atoll. Modern reef building corals are composed mostly of the calcium carbonate chiefly in the form of aragonite. The effect of the bomb detonation was to heat and throw aloft a huge amount of coral dust, Most of the coral dust which was close enough to the explosion to become contaminated with radioactivity was heated sufficiently to drive off carvcn dioxide and to form calcium oxide. These calcium oxide particles swent off the condensing fission products which were probably in the form of very small metallic or metallic oxide particles. At some subsequent time, as the cloud cooled, the calcium oxide hydrated to calcium hydroxide. This could easily have occurred while the particles were still in the air since large amounts of sea water were evaporated and blown into the air by the explosion. In some cases, the hydration was not complete as shown by the examples of several particles still retaining cores of unaltered calcium oxide, Probably during the hydration process a part of the soluble frac- tion of the radioactive material went into sdlution and diffused into the particle leaving a zone of radioactivity which was most intense on the surface and diminished gradually to very lew levele within a distance of about 100 pe 98