UNCLASSIFIED ee cee oO eee calculation of an average activity per slurry particle, and an estimate of the average volume and weight of insoluble solids per particle by the standard spot comparison method, The two independent methods gave an average value for Flathead of 1x 1013 ¢/m/g at H + 12 in the well counter, The latter method only was used for Navajo, resulting in a value of 1 x 10°* solids, c/m/g of insoluble Table 2 presents experimental data on the total activity per unit area for the two events for various stations. These data are in terms of a count (at H + 12) in the crystal well counter. The total mass of sodium chloride per unit area is a calculated value obtained by dividing the total activity per unit area for a given station (Table 2) by the average activity per NaCl mass (Table 1). Sodium chloride represents the major solid mass of fallout, Since the water content depends on the humidity conditions through which the particle passed, the weight of water is not considered a part of fallout mass. However, if one wishes to compute the approximate weight of water, one multiplies the mass of NaCl by 1.2, which is the average weight ratio of water to NaCl. A plot of the dependent variables, activity per unit area versus NaCl mass per unit area, presents Table 2 data as a necessarily smooth curve (Fig.3). With this plot one can roughly deduce relative activity by a measure of sodium chloride per square foot or the converse, The very high initial values of sodium chloride mass per square foot have not been plotted on the curve, DISCUSSION The particle densities (Table 1) cluster about a mean value which is nearly the same for both events, The mean density for the l= to 3-hr period is close to the overall mean value. By whatever means the ratio of water to solids reaches equilibrium, this mechanism is fairly rapid, Equilibrium has been reached by the time the particle lands. In Navajo there appears to be a sharp decrease in density after H+13. This time corresponds to the after-sunset hours when changes in ambient atmospheric conditions might be expected. The particle size (Table 1, "Navajo") generally decreases with time, although it is noteworthy that there is little droplet size variation in 15 hr, For any given time period, one need not discuss particle size distribution since the standard deviation of the mean diameter is so small... -10- x= £ EF A B EF ££ FF 2 & ot ak UO a a UNCLASSIFIED