the surface in others (Figure 3.18). It may also be seen that the overall variation of activity with size is controlled by the irregular particles, which appear to predominate numerically in the fallout (Table B.9), rather than by the spheroidal particles. Table 3.11 illustrates how the activity in each Size group was divided among the three particle types. No correlation of particle activity with density was possible (Figure 3.25) but a rough relationship with weight was derived for a group of Tewa particles from the YFNB 29 on the basis of Figure 3.24: Ac w"'' where W refers to the weight in micrograms and nonregression error is estimated at ~ 140 percent (Reference 25). (An additional study was performed at NRDL, using 57 particles from the Same source and a more Stable microbalance. The result- ing relation was: A < W°'".) This result is consistent with the diameter functions, because p'« w. The relative activities of the white and yellow spheroidal particles referred to ear- lier were also compared and the latter were found to be slightly more active than the former. 3.3.2 Slurry Particles. All of the fallout collected during Shots Flathead and Navajo consisted of slurry particles whose inert components were water, sea salts, and a small amount of insoluble solids. (Although IC and SIC trays containing greased disks were interspersed among those containing reagent films for shots, no isolated solid particles that were active were observed.) Large crystals displaying the characteristic cubic shape of sodium chloride were occasionally observed in suspension. The physical and chemical, radiochemical, and radiation characteristics of these particles are discussed below. Table B.35 contains representative sets of data, including data on particles collected on the YAG 40 and at several other stations during each shot. Physical and Chemical Characteristics. Slurry particles have been studied extensively and are discussed in detail in Reference 31. The results of preliminary studies of the insoluble solids contained in such particles are given in Reference 32. Figure 3.28 ig a photomicrograph of a typical deposited slurry droplet, after reaction with the chloride-sensitive reagent film surface. The chloride-reaction area appears as a white disk, while the trace or impression of the impinging drop is egg shaped and encloses the insoluble solids. The concentric rings are thought to be a Liesegang phenomenon. An electronmicrograph of a portion of the solids is shown in Figure 3.29, illustrating the typical dense agglomeration of small spheres and irregular particles. The physical properties of the droplets were established in part by microscopic examination in the YAG 40 laboratory soon after their arrival, and in part by subsequent measurements and calculations. For example, the dimensions of the droplets that appeared on the greased trays provided a rapid approximation of drop diameter, but the sphere diameters reported in Table 3.12 were calculated from the amount of chloride (reported as NaCl equivalent) and H,O meas- ured later from the reagent films. It will be noted that particle size decreased very slowly with time; and that for any given time period, size distribution need not be considered, because stand- ard deviations are small. Average densities for the slurry particles, calculated from their di- mensions and the masses of NaCl and H,O present, are also given in Table 3.12. On the basis of the data in Table 3.12, and a calibration method for solids volumethat inVolved the collection on reagent film of simulated slurry droplets containing aluminum oxide Suspensions of appropriate diameter at known concentrations, it was estimated that the particles Were about 80 percent NaCl, 18 percent H,O, and 2 percent insoluble solids by volume. The latter were generally amber in color and appeared under high magnification (Figure 3.29) to be *gZlomerates composed of irregular and spherical solids ranging in size from about 15 microns to less than 0.1:micron in diameter. The greatest number of these solids were spherical and mic than 1 micron in diameter, although a few were observed in the size range from 15 to 60 Tons, Chemical properties were determined by chloride reagent film, X-ray diffraction, and elec- °n diffraction techniques. (The gross chemistry of slurry drops is of course implicit in the 4nalyses of the OCC collections from Shots Flathead and Navajo (Table B.18); no attempt has conta to determine the extent of correlation.) The first featured the use of a gelatin film ining colloidal red silver dichromate, with which the soluble halides deposited on the film 53