30 T | | T ZY ] Yy F207 ], - SL UW _ V 5 A), oy 160 yyy YY; «3320.2 4BO—S—«a AO AVERAGE PARTICLE SIZE, um Figure 4, Activity vs granule size for Bikini ash. function. This simple power function model gave a best fit to the results recorded by Norment. Tsuzuki reported the observed fallout arrival time, cessation time, and granule size distribution for Bikini Ash (Ts55). These data were used to model a power function relationship which related granule size to granule fall time specifically for BRAVO fallout as follows: where T= 79.5 pO-524 | (2) T * granule fall time in hours post-BRAVO, D = granule size, micrometers. It was assumed by us that the largest granules in the Bikini ash fell upon arrival and the smallest fell upon cessation of fallout. We used Eq. (2) to determine granule size distribution at Rongelap, Utirik, and Sifo Islands. To deter- - 24 =