(1) Percentage of solids by weight - Island shot samples show a much higher percentage of solids than do barge shots, with Shot 1 samples having a higher percentage than Shot 3. No quantitative corre~ lations based on per cent solids can be made because of the variable volume of water. (2) pH = Island shot samples had the high pH characteristic of suspensions of alkaline earth hydrcxides. CaO or Ca(OH)» was present in the fallout as a product of the pyrolyzation of CaCO3, from the island coral which had been drawn up into the fireball. The fallout samples from the island shots consisting of both solid and liquid usually contained enough of the hydroxide +o maintain a solid-liquid equilibrium, The pH of the liquid from barge shots was fairly close to the pH of sea water itself. (3) Gamma Activity Fractionation ~ Where the solids were pres- ent in large percentages (island shots), most of the gamma activity was found in the solid fraction. On the other hand, for barge shots most of the activity was in the ionic fraction. It should be noted that for every cample treated (both island and barge shots) the liquid fraction itself was 96.1 to 97.5 per cent ionic. The constancy of this figure suggests that the material held by the filter membrane was not colloidal since the percentage of colloids in the liquid samples should depend on when the samples were treated and should also vary from sample to sample ard shot to shot. It is more likely that a constant percentage of the liquid activity is adsorbed by the membrane. Whatever constituted the so-called colloidal fraction, it. was never very important in the samples as analyzed, for the gamma activity in this fraction was never higher than 2.4 per cent of the total sample. The small percentage found, however, does not necessarily mean that there was originally such small amounts of gamma activity associated with a colloidal fraction in the fallout itself. colloid Disappearance of a which may have occurred originally in the fallout could be explained by: either (1) agglomeration of colloidal particles with time in the presence of rather high concentrations of electrolyte, or (2) adsorption of colloidal particles on crystalline materials or on the walls of the sample bottle. The centrifugation separation would not distinguish between particles which were large enough to settle in a centrifugal field and colloidal-sized particles which were associated with crystalline solids. A very early collection and analysis of liquid fallout material for detonations which might produce a liquid phase fallout would serve to determine whether colloidal particles are present and whether they do indeed agglomerate at appreciable rates. In terms of particle size, the colloid cannot be disregarded in estimating contamination potential of the fallout unless it can be conclusively shown that they do not exist at the time the fallout contacts a surface. 302.202 Gamma Decay of Physical State Fractions Decay for the three fractions and the original slurry are given in Figs. 3.1 through 3.4 for some of the semples separated. To aid in the comparison of the fractions for a given sample, all counts were normalized to.1000 at the earliest possible time. Where a decay curve was 36