The fact that the mesn particle diameter at Ailinginae is smaller than et Rongelap cen be partially explained byanalysis of the wind profile which indicates, as one moves south from the axis of symmetry of the fellout pattern, that. the particles delivered have smaller diameters (see Chapter 6). 5.2.2 Shot 6, Particle Size The differential collector stationed on Alice contained visible particulate as well as some liquid; the anelysis of particle size distribution 1s presented in Appendix C. With a total of 321 particles measured the distribution was nearly log norm2l with a geometric mean diameter of 180 bh es shown in Fig. 5.8. Alice was 3 nautical niles from ground zero. , . RATIO OF ACTIVE TO INACTIVE PARTICLES One of the most difficult problems to resolve is the ratio of active to inactive fallout particles that arrive at a collecting irstrument. This is especially true of the smaller diameter particles because it is extremely difficult to avoid pollution of the sample hy extraneous particulate. In this anelysis many small insctive particles were observed during the measurement of rarticle diameters. in many cases these parti- cles were Jess than 5 # in diameter, To arrive at a ratio, all particulate was ignored that, did not have the characteristic white opaque color of fallout. Two samples were analyzed from Shot 1 fallout collected at lagoon stations where the effect of island dust pollution was minimized. The results are shorn in Fig. 5.9 Approximetely 25 per cent of the parti- cles were found to be inective with the mean particle size of the in- active particles smaller than the active. 5.4 PARTICLE DENSITY Particles from the Shot 1 legcon station differential fallout collectors were analyzed to determine their apparent. density which is defined as the specific gravity of the particle as a whole. Because of the station locations and the collecting instrument used, these particles hac a very high probability of being true fallout. Seventy-nine particles from stations 250.04, 250.17, and 250.°4 were measured. Density, average clameter, color, and relative activity were determined for each particle. Table 5.5 shows the particle density found at each station. The overall averare density of the 79 particles was 2.36 g/cu cm with a standard deviation of 8.9 per cent. Attempts to find relationships between particle size ‘and activity; particle size and density; and density and activity proved unsuccessful. All particle density data are tabulated in Appendix D. 4 §.3